Node.js v25.8.0 documentation

Command-line API#

Node.js comes with a variety of CLI options. These options expose built-in debugging, multiple ways to execute scripts, and other helpful runtime options.

To view this documentation as a manual page in a terminal, run man node.

Synopsis#

node [options] [V8 options] [<program-entry-point> | -e "script" | -] [--] [arguments]

node inspect [<program-entry-point> | -e "script" | <host>:<port>] …

node --v8-options

Execute without arguments to start the REPL.

For more info about node inspect, see the debugger documentation.

Program entry point#

The program entry point is a specifier-like string. If the string is not an absolute path, it's resolved as a relative path from the current working directory. That entry point string is then resolved as if it's been requested by require() from the current working directory. If no corresponding file is found, an error is thrown.

By default, the resolved path is also loaded as if it's been requested by require(), unless one of the conditions below apply—then it's loaded as if it's been requested by import():

• The program was started with a command-line flag that forces the entry point to be loaded with ECMAScript module loader, such as --import.
• The file has an .mjs, .mts or .wasm extension.
• The file does not have a .cjs extension, and the nearest parent package.json file contains a top-level "type" field with a value of "module".

See module resolution and loading for more details.

Options#

All options, including V8 options, allow words to be separated by both dashes (-) or underscores (_). For example, --pending-deprecation is equivalent to --pending_deprecation.

If an option that takes a single value (such as --max-http-header-size) is passed more than once, then the last passed value is used. Options from the command line take precedence over options passed through the NODE_OPTIONS environment variable.

Alias for stdin. Analogous to the use of - in other command-line utilities, meaning that the script is read from stdin, and the rest of the options are passed to that script.

Indicate the end of node options. Pass the rest of the arguments to the script. If no script filename or eval/print script is supplied prior to this, then the next argument is used as a script filename.

--abort-on-uncaught-exception#

Aborting instead of exiting causes a core file to be generated for post-mortem analysis using a debugger (such as lldb, gdb, and mdb).

If this flag is passed, the behavior can still be set to not abort through process.setUncaughtExceptionCaptureCallback() (and through usage of the node:domain module that uses it).

--allow-addons#

When using the Permission Model, the process will not be able to use native addons by default. Attempts to do so will throw an ERR_DLOPEN_DISABLED unless the user explicitly passes the --allow-addons flag when starting Node.js.

Example:

// Attempt to require an native addon
require('nodejs-addon-example');
copy

$ node --permission --allow-fs-read=* index.js
node:internal/modules/cjs/loader:1319
  return process.dlopen(module, path.toNamespacedPath(filename));
                 ^

Error: Cannot load native addon because loading addons is disabled.
    at Module._extensions..node (node:internal/modules/cjs/loader:1319:18)
    at Module.load (node:internal/modules/cjs/loader:1091:32)
    at Module._load (node:internal/modules/cjs/loader:938:12)
    at Module.require (node:internal/modules/cjs/loader:1115:19)
    at require (node:internal/modules/helpers:130:18)
    at Object.<anonymous> (/home/index.js:1:15)
    at Module._compile (node:internal/modules/cjs/loader:1233:14)
    at Module._extensions..js (node:internal/modules/cjs/loader:1287:10)
    at Module.load (node:internal/modules/cjs/loader:1091:32)
    at Module._load (node:internal/modules/cjs/loader:938:12) {
  code: 'ERR_DLOPEN_DISABLED'
}
copy

--allow-child-process#

When using the Permission Model, the process will not be able to spawn any child process by default. Attempts to do so will throw an ERR_ACCESS_DENIED unless the user explicitly passes the --allow-child-process flag when starting Node.js.

Example:

const childProcess = require('node:child_process');
// Attempt to bypass the permission
childProcess.spawn('node', ['-e', 'require("fs").writeFileSync("/new-file", "example")']);
copy

$ node --permission --allow-fs-read=* index.js
node:internal/child_process:388
  const err = this._handle.spawn(options);
                           ^
Error: Access to this API has been restricted
    at ChildProcess.spawn (node:internal/child_process:388:28)
    at node:internal/main/run_main_module:17:47 {
  code: 'ERR_ACCESS_DENIED',
  permission: 'ChildProcess'
}
copy

The child_process.fork() API inherits the execution arguments from the parent process. This means that if Node.js is started with the Permission Model enabled and the --allow-child-process flag is set, any child process created using child_process.fork() will automatically receive all relevant Permission Model flags.

This behavior also applies to child_process.spawn(), but in that case, the flags are propagated via the NODE_OPTIONS environment variable rather than directly through the process arguments.

--allow-fs-read#

This flag configures file system read permissions using the Permission Model.

The valid arguments for the --allow-fs-read flag are:

• * - To allow all FileSystemRead operations.
• Multiple paths can be allowed using multiple --allow-fs-read flags. Example --allow-fs-read=/folder1/ --allow-fs-read=/folder1/

Examples can be found in the File System Permissions documentation.

The initializer module and custom --require modules has a implicit read permission.

$ node --permission -r custom-require.js -r custom-require-2.js index.js
copy

• The custom-require.js, custom-require-2.js, and index.js will be by default in the allowed read list.

process.has('fs.read', 'index.js'); // true
process.has('fs.read', 'custom-require.js'); // true
process.has('fs.read', 'custom-require-2.js'); // true
copy

--allow-fs-write#

This flag configures file system write permissions using the Permission Model.

The valid arguments for the --allow-fs-write flag are:

• * - To allow all FileSystemWrite operations.
• Multiple paths can be allowed using multiple --allow-fs-write flags. Example --allow-fs-write=/folder1/ --allow-fs-write=/folder1/

Paths delimited by comma (,) are no longer allowed. When passing a single flag with a comma a warning will be displayed.

Examples can be found in the File System Permissions documentation.

--allow-inspector#

When using the Permission Model, the process will not be able to connect through inspector protocol.

Attempts to do so will throw an ERR_ACCESS_DENIED unless the user explicitly passes the --allow-inspector flag when starting Node.js.

Example:

const { Session } = require('node:inspector/promises');

const session = new Session();
session.connect();
copy

$ node --permission index.js
Error: connect ERR_ACCESS_DENIED Access to this API has been restricted. Use --allow-inspector to manage permissions.
  code: 'ERR_ACCESS_DENIED',
}
copy

--allow-net#

When using the Permission Model, the process will not be able to access network by default. Attempts to do so will throw an ERR_ACCESS_DENIED unless the user explicitly passes the --allow-net flag when starting Node.js.

Example:

const http = require('node:http');
// Attempt to bypass the permission
const req = http.get('http://example.com', () => {});

req.on('error', (err) => {
  console.log('err', err);
});
copy

$ node --permission index.js
Error: connect ERR_ACCESS_DENIED Access to this API has been restricted. Use --allow-net to manage permissions.
  code: 'ERR_ACCESS_DENIED',
}
copy

--allow-wasi#

When using the Permission Model, the process will not be capable of creating any WASI instances by default. For security reasons, the call will throw an ERR_ACCESS_DENIED unless the user explicitly passes the flag --allow-wasi in the main Node.js process.

Example:

const { WASI } = require('node:wasi');
// Attempt to bypass the permission
new WASI({
  version: 'preview1',
  // Attempt to mount the whole filesystem
  preopens: {
    '/': '/',
  },
});
copy

$ node --permission --allow-fs-read=* index.js

Error: Access to this API has been restricted
    at node:internal/main/run_main_module:30:49 {
  code: 'ERR_ACCESS_DENIED',
  permission: 'WASI',
}
copy

--allow-worker#

When using the Permission Model, the process will not be able to create any worker threads by default. For security reasons, the call will throw an ERR_ACCESS_DENIED unless the user explicitly pass the flag --allow-worker in the main Node.js process.

Example:

const { Worker } = require('node:worker_threads');
// Attempt to bypass the permission
new Worker(__filename);
copy

$ node --permission --allow-fs-read=* index.js

Error: Access to this API has been restricted
    at node:internal/main/run_main_module:17:47 {
  code: 'ERR_ACCESS_DENIED',
  permission: 'WorkerThreads'
}
copy

--build-sea=config#

Generates a single executable application from a JSON configuration file. The argument must be a path to the configuration file. If the path is not absolute, it is resolved relative to the current working directory.

For configuration fields, cross-platform notes, and asset APIs, see the single executable application documentation.

--build-snapshot#

Generates a snapshot blob when the process exits and writes it to disk, which can be loaded later with --snapshot-blob.

When building the snapshot, if --snapshot-blob is not specified, the generated blob will be written, by default, to snapshot.blob in the current working directory. Otherwise it will be written to the path specified by --snapshot-blob.

$ echo "globalThis.foo = 'I am from the snapshot'" > snapshot.js

# Run snapshot.js to initialize the application and snapshot the
# state of it into snapshot.blob.
$ node --snapshot-blob snapshot.blob --build-snapshot snapshot.js

$ echo "console.log(globalThis.foo)" > index.js

# Load the generated snapshot and start the application from index.js.
$ node --snapshot-blob snapshot.blob index.js
I am from the snapshot
copy

The v8.startupSnapshot API can be used to specify an entry point at snapshot building time, thus avoiding the need of an additional entry script at deserialization time:

$ echo "require('v8').startupSnapshot.setDeserializeMainFunction(() => console.log('I am from the snapshot'))" > snapshot.js
$ node --snapshot-blob snapshot.blob --build-snapshot snapshot.js
$ node --snapshot-blob snapshot.blob
I am from the snapshot
copy

For more information, check out the v8.startupSnapshot API documentation.

The snapshot currently only supports loding a single entrypoint during the snapshot building process, which can load built-in modules, but not additional user-land modules. Users can bundle their applications into a single script with their bundler of choice before building a snapshot.

As it's complicated to ensure the serializablility of all built-in modules, which are also growing over time, only a subset of the built-in modules are well tested to be serializable during the snapshot building process. The Node.js core test suite checks that a few fairly complex applications can be snapshotted. The list of built-in modules being captured by the built-in snapshot of Node.js is considered supported. When the snapshot builder encounters a built-in module that cannot be serialized, it may crash the snapshot building process. In that case a typical workaround would be to delay loading that module until runtime, using either v8.startupSnapshot.setDeserializeMainFunction() or v8.startupSnapshot.addDeserializeCallback(). If serialization for an additional module during the snapshot building process is needed, please file a request in the Node.js issue tracker and link to it in the tracking issue for user-land snapshots.

--build-snapshot-config#

Specifies the path to a JSON configuration file which configures snapshot creation behavior.

The following options are currently supported:

• builder <string> Required. Provides the name to the script that is executed before building the snapshot, as if --build-snapshot had been passed with builder as the main script name.
• withoutCodeCache <boolean> Optional. Including the code cache reduces the time spent on compiling functions included in the snapshot at the expense of a bigger snapshot size and potentially breaking portability of the snapshot.

When using this flag, additional script files provided on the command line will not be executed and instead be interpreted as regular command line arguments.

-c, --check#

Syntax check the script without executing.

--completion-bash#

Print source-able bash completion script for Node.js.

node --completion-bash > node_bash_completion
source node_bash_completion
copy

-C condition, --conditions=condition#

Provide custom conditional exports resolution conditions.

Any number of custom string condition names are permitted.

The default Node.js conditions of "node", "default", "import", and "require" will always apply as defined.

For example, to run a module with "development" resolutions:

node -C development app.js
copy

--cpu-prof#

Starts the V8 CPU profiler on start up, and writes the CPU profile to disk before exit.

If --cpu-prof-dir is not specified, the generated profile is placed in the current working directory.

If --cpu-prof-name is not specified, the generated profile is named CPU.${yyyymmdd}.${hhmmss}.${pid}.${tid}.${seq}.cpuprofile.

$ node --cpu-prof index.js
$ ls *.cpuprofile
CPU.20190409.202950.15293.0.0.cpuprofile
copy

If --cpu-prof-name is specified, the provided value is used as a template for the file name. The following placeholder is supported and will be substituted at runtime:

• ${pid} — the current process ID

$ node --cpu-prof --cpu-prof-name 'CPU.${pid}.cpuprofile' index.js
$ ls *.cpuprofile
CPU.15293.cpuprofile
copy

--cpu-prof-dir#

Specify the directory where the CPU profiles generated by --cpu-prof will be placed.

The default value is controlled by the --diagnostic-dir command-line option.

--cpu-prof-interval#

Specify the sampling interval in microseconds for the CPU profiles generated by --cpu-prof. The default is 1000 microseconds.

--cpu-prof-name#

Specify the file name of the CPU profile generated by --cpu-prof.

--diagnostic-dir=directory#

Set the directory to which all diagnostic output files are written. Defaults to current working directory.

Affects the default output directory of:

• --cpu-prof-dir
• --heap-prof-dir
• --redirect-warnings

--disable-proto=mode#

Disable the Object.prototype.__proto__ property. If mode is delete, the property is removed entirely. If mode is throw, accesses to the property throw an exception with the code ERR_PROTO_ACCESS.

--disable-sigusr1#

Disable the ability of starting a debugging session by sending a SIGUSR1 signal to the process.

--disable-warning=code-or-type#

Disable specific process warnings by code or type.

Warnings emitted from process.emitWarning() may contain a code and a type. This option will not-emit warnings that have a matching code or type.

List of deprecation warnings.

The Node.js core warning types are: DeprecationWarning and ExperimentalWarning

For example, the following script will not emit DEP0025 require('node:sys') when executed with node --disable-warning=DEP0025:

import sys from 'node:sys';
const sys = require('node:sys');
copy

For example, the following script will emit the DEP0025 require('node:sys'), but not any Experimental Warnings (such as ExperimentalWarning: vm.measureMemory is an experimental feature in <=v21) when executed with node --disable-warning=ExperimentalWarning:

import sys from 'node:sys';
import vm from 'node:vm';

vm.measureMemory();
const sys = require('node:sys');
const vm = require('node:vm');

vm.measureMemory();
copy

--disable-wasm-trap-handler#

By default, Node.js enables trap-handler-based WebAssembly bound checks. As a result, V8 does not need to insert inline bound checks in the code compiled from WebAssembly which may speed up WebAssembly execution significantly, but this optimization requires allocating a big virtual memory cage (currently 10GB). If the Node.js process does not have access to a large enough virtual memory address space due to system configurations or hardware limitations, users won't be able to run any WebAssembly that involves allocation in this virtual memory cage and will see an out-of-memory error.

$ ulimit -v 5000000
$ node -p "new WebAssembly.Memory({ initial: 10, maximum: 100 });"
[eval]:1
new WebAssembly.Memory({ initial: 10, maximum: 100 });
^

RangeError: WebAssembly.Memory(): could not allocate memory
    at [eval]:1:1
    at runScriptInThisContext (node:internal/vm:209:10)
    at node:internal/process/execution:118:14
    at [eval]-wrapper:6:24
    at runScript (node:internal/process/execution:101:62)
    at evalScript (node:internal/process/execution:136:3)
    at node:internal/main/eval_string:49:3

copy

--disable-wasm-trap-handler disables this optimization so that users can at least run WebAssembly (with less optimal performance) when the virtual memory address space available to their Node.js process is lower than what the V8 WebAssembly memory cage needs.

--disallow-code-generation-from-strings#

Make built-in language features like eval and new Function that generate code from strings throw an exception instead. This does not affect the Node.js node:vm module.

--dns-result-order=order#

Set the default value of order in dns.lookup() and dnsPromises.lookup(). The value could be:

• ipv4first: sets default order to ipv4first.
• ipv6first: sets default order to ipv6first.
• verbatim: sets default order to verbatim.

The default is verbatim and dns.setDefaultResultOrder() have higher priority than --dns-result-order.

--enable-fips#

Enable FIPS-compliant crypto at startup. (Requires Node.js to be built against FIPS-compatible OpenSSL.)

--enable-source-maps#

Enable Source Map support for stack traces.

When using a transpiler, such as TypeScript, stack traces thrown by an application reference the transpiled code, not the original source position. --enable-source-maps enables caching of Source Maps and makes a best effort to report stack traces relative to the original source file.

Overriding Error.prepareStackTrace may prevent --enable-source-maps from modifying the stack trace. Call and return the results of the original Error.prepareStackTrace in the overriding function to modify the stack trace with source maps.

const originalPrepareStackTrace = Error.prepareStackTrace;
Error.prepareStackTrace = (error, trace) => {
  // Modify error and trace and format stack trace with
  // original Error.prepareStackTrace.
  return originalPrepareStackTrace(error, trace);
};
copy

Note, enabling source maps can introduce latency to your application when Error.stack is accessed. If you access Error.stack frequently in your application, take into account the performance implications of --enable-source-maps.

--entry-url#

When present, Node.js will interpret the entry point as a URL, rather than a path.

Follows ECMAScript module resolution rules.

Any query parameter or hash in the URL will be accessible via import.meta.url.

node --entry-url 'file:///path/to/file.js?queryparams=work#and-hashes-too'
node --entry-url 'file.ts?query#hash'
node --entry-url 'data:text/javascript,console.log("Hello")'
copy

--env-file-if-exists=file#

Behavior is the same as --env-file, but an error is not thrown if the file does not exist.

--env-file=file#

Loads environment variables from a file relative to the current directory, making them available to applications on process.env. The environment variables which configure Node.js, such as NODE_OPTIONS, are parsed and applied. If the same variable is defined in the environment and in the file, the value from the environment takes precedence.

You can pass multiple --env-file arguments. Subsequent files override pre-existing variables defined in previous files.

An error is thrown if the file does not exist.

node --env-file=.env --env-file=.development.env index.js
copy

The format of the file should be one line per key-value pair of environment variable name and value separated by =:

PORT=3000
copy

Any text after a # is treated as a comment:

# This is a comment
PORT=3000 # This is also a comment
copy

Values can start and end with the following quotes: `, " or '. They are omitted from the values.

USERNAME="nodejs" # will result in `nodejs` as the value.
copy

Multi-line values are supported:

MULTI_LINE="THIS IS
A MULTILINE"
# will result in `THIS IS\nA MULTILINE` as the value.
copy

Export keyword before a key is ignored:

export USERNAME="nodejs" # will result in `nodejs` as the value.
copy

If you want to load environment variables from a file that may not exist, you can use the --env-file-if-exists flag instead.

-e, --eval "script"#

Evaluate the following argument as JavaScript. The modules which are predefined in the REPL can also be used in script.

On Windows, using cmd.exe a single quote will not work correctly because it only recognizes double " for quoting. In Powershell or Git bash, both ' and " are usable.

It is possible to run code containing inline types unless the --no-strip-types flag is provided.

--experimental-addon-modules#

Enable experimental import support for .node addons.

--experimental-config-file=config#

If present, Node.js will look for a configuration file at the specified path. Node.js will read the configuration file and apply the settings. The configuration file should be a JSON file with the following structure. vX.Y.Z in the $schema must be replaced with the version of Node.js you are using.

{
  "$schema": "https://nodejs.org/dist/vX.Y.Z/docs/node-config-schema.json",
  "nodeOptions": {
    "import": [
      "amaro/strip"
    ],
    "watch-path": "src",
    "watch-preserve-output": true
  },
  "test": {
    "test-isolation": "process"
  },
  "watch": {
    "watch-preserve-output": true
  }
}
copy

The configuration file supports namespace-specific options:

• The nodeOptions field contains CLI flags that are allowed in NODE_OPTIONS.

• Namespace fields like test, watch, and permission contain configuration specific to that subsystem.

When a namespace is present in the configuration file, Node.js automatically enables the corresponding flag (e.g., --test, --watch, --permission). This allows you to configure subsystem-specific options without explicitly passing the flag on the command line.

For example:

{
  "test": {
    "test-isolation": "process"
  }
}
copy

is equivalent to:

node --test --test-isolation=process
copy

To disable the automatic flag while still using namespace options, you can explicitly set the flag to false within the namespace:

{
  "test": {
    "test": false,
    "test-isolation": "process"
  }
}
copy

No-op flags are not supported. Not all V8 flags are currently supported.

It is possible to use the official JSON schema to validate the configuration file, which may vary depending on the Node.js version. Each key in the configuration file corresponds to a flag that can be passed as a command-line argument. The value of the key is the value that would be passed to the flag.

For example, the configuration file above is equivalent to the following command-line arguments:

node --import amaro/strip --watch-path=src --watch-preserve-output --test-isolation=process
copy

The priority in configuration is as follows:

1. NODE_OPTIONS and command-line options
2. Configuration file
3. Dotenv NODE_OPTIONS

Values in the configuration file will not override the values in the environment variables and command-line options, but will override the values in the NODE_OPTIONS env file parsed by the --env-file flag.

Keys cannot be duplicated within the same or different namespaces.

The configuration parser will throw an error if the configuration file contains unknown keys or keys that cannot be used in a namespace.

Node.js will not sanitize or perform validation on the user-provided configuration, so NEVER use untrusted configuration files.

--experimental-default-config-file#

If the --experimental-default-config-file flag is present, Node.js will look for a node.config.json file in the current working directory and load it as a as configuration file.

--experimental-eventsource#

Enable exposition of EventSource Web API on the global scope.

--experimental-import-meta-resolve#

Enable experimental import.meta.resolve() parent URL support, which allows passing a second parentURL argument for contextual resolution.

Previously gated the entire import.meta.resolve feature.

--experimental-inspector-network-resource#

Enable experimental support for inspector network resources.

--experimental-loader=module#

This flag is discouraged and may be removed in a future version of Node.js. Please use --import with register() instead.

Specify the module containing exported asynchronous module customization hooks. module may be any string accepted as an import specifier.

This feature requires --allow-worker if used with the Permission Model.

--experimental-network-inspection#

Enable experimental support for the network inspection with Chrome DevTools.

--experimental-print-required-tla#

If the ES module being require()'d contains top-level await, this flag allows Node.js to evaluate the module, try to locate the top-level awaits, and print their location to help users find them.

--experimental-quic#

Enable experimental support for the QUIC protocol.

--experimental-sea-config#

Use this flag to generate a blob that can be injected into the Node.js binary to produce a single executable application. See the documentation about this configuration for details.

--experimental-shadow-realm#

Use this flag to enable ShadowRealm support.

--experimental-storage-inspection#

Enable experimental support for storage inspection

--experimental-test-coverage#

When used in conjunction with the node:test module, a code coverage report is generated as part of the test runner output. If no tests are run, a coverage report is not generated. See the documentation on collecting code coverage from tests for more details.

--experimental-test-module-mocks#

Enable module mocking in the test runner.

This feature requires --allow-worker if used with the Permission Model.

--experimental-transform-types#

Enables the transformation of TypeScript-only syntax into JavaScript code. Implies --enable-source-maps.

--experimental-vm-modules#

Enable experimental ES Module support in the node:vm module.

--experimental-wasi-unstable-preview1#

Enable experimental WebAssembly System Interface (WASI) support.

--experimental-worker-inspection#

Enable experimental support for the worker inspection with Chrome DevTools.

--expose-gc#

This flag will expose the gc extension from V8.

if (globalThis.gc) {
  globalThis.gc();
}
copy

--force-context-aware#

Disable loading native addons that are not context-aware.

--force-fips#

Force FIPS-compliant crypto on startup. (Cannot be disabled from script code.) (Same requirements as --enable-fips.)

--force-node-api-uncaught-exceptions-policy#

Enforces uncaughtException event on Node-API asynchronous callbacks.

To prevent from an existing add-on from crashing the process, this flag is not enabled by default. In the future, this flag will be enabled by default to enforce the correct behavior.

--frozen-intrinsics#

Enable experimental frozen intrinsics like Array and Object.

Only the root context is supported. There is no guarantee that globalThis.Array is indeed the default intrinsic reference. Code may break under this flag.

To allow polyfills to be added, --require and --import both run before freezing intrinsics.

--heap-prof#

Starts the V8 heap profiler on start up, and writes the heap profile to disk before exit.

If --heap-prof-dir is not specified, the generated profile is placed in the current working directory.

If --heap-prof-name is not specified, the generated profile is named Heap.${yyyymmdd}.${hhmmss}.${pid}.${tid}.${seq}.heapprofile.

$ node --heap-prof index.js
$ ls *.heapprofile
Heap.20190409.202950.15293.0.001.heapprofile
copy

--heap-prof-dir#

Specify the directory where the heap profiles generated by --heap-prof will be placed.

The default value is controlled by the --diagnostic-dir command-line option.

--heap-prof-interval#

Specify the average sampling interval in bytes for the heap profiles generated by --heap-prof. The default is 512 * 1024 bytes.

--heap-prof-name#

Specify the file name of the heap profile generated by --heap-prof.

--heapsnapshot-near-heap-limit=max_count#

Writes a V8 heap snapshot to disk when the V8 heap usage is approaching the heap limit. count should be a non-negative integer (in which case Node.js will write no more than max_count snapshots to disk).

When generating snapshots, garbage collection may be triggered and bring the heap usage down. Therefore multiple snapshots may be written to disk before the Node.js instance finally runs out of memory. These heap snapshots can be compared to determine what objects are being allocated during the time consecutive snapshots are taken. It's not guaranteed that Node.js will write exactly max_count snapshots to disk, but it will try its best to generate at least one and up to max_count snapshots before the Node.js instance runs out of memory when max_count is greater than 0.

Generating V8 snapshots takes time and memory (both memory managed by the V8 heap and native memory outside the V8 heap). The bigger the heap is, the more resources it needs. Node.js will adjust the V8 heap to accommodate the additional V8 heap memory overhead, and try its best to avoid using up all the memory available to the process. When the process uses more memory than the system deems appropriate, the process may be terminated abruptly by the system, depending on the system configuration.

$ node --max-old-space-size=100 --heapsnapshot-near-heap-limit=3 index.js
Wrote snapshot to Heap.20200430.100036.49580.0.001.heapsnapshot
Wrote snapshot to Heap.20200430.100037.49580.0.002.heapsnapshot
Wrote snapshot to Heap.20200430.100038.49580.0.003.heapsnapshot

<--- Last few GCs --->

[49580:0x110000000]     4826 ms: Mark-sweep 130.6 (147.8) -> 130.5 (147.8) MB, 27.4 / 0.0 ms  (average mu = 0.126, current mu = 0.034) allocation failure scavenge might not succeed
[49580:0x110000000]     4845 ms: Mark-sweep 130.6 (147.8) -> 130.6 (147.8) MB, 18.8 / 0.0 ms  (average mu = 0.088, current mu = 0.031) allocation failure scavenge might not succeed


<--- JS stacktrace --->

FATAL ERROR: Ineffective mark-compacts near heap limit Allocation failed - JavaScript heap out of memory
....
copy

--heapsnapshot-signal=signal#

Enables a signal handler that causes the Node.js process to write a heap dump when the specified signal is received. signal must be a valid signal name. Disabled by default.

$ node --heapsnapshot-signal=SIGUSR2 index.js &
$ ps aux
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
node         1  5.5  6.1 787252 247004 ?       Ssl  16:43   0:02 node --heapsnapshot-signal=SIGUSR2 index.js
$ kill -USR2 1
$ ls
Heap.20190718.133405.15554.0.001.heapsnapshot
copy

-h, --help#

Print node command-line options. The output of this option is less detailed than this document.

--icu-data-dir=file#

Specify ICU data load path. (Overrides NODE_ICU_DATA.)

--import=module#

Preload the specified module at startup. If the flag is provided several times, each module will be executed sequentially in the order they appear, starting with the ones provided in NODE_OPTIONS.

Follows ECMAScript module resolution rules. Use --require to load a CommonJS module. Modules preloaded with --require will run before modules preloaded with --import.

Modules are preloaded into the main thread as well as any worker threads, forked processes, or clustered processes.

--input-type=type#

This configures Node.js to interpret --eval or STDIN input as CommonJS or as an ES module. Valid values are "commonjs", "module", "module-typescript" and "commonjs-typescript". The "-typescript" values are not available with the flag --no-strip-types. The default is no value, or "commonjs" if --no-experimental-detect-module is passed.

If --input-type is not provided, Node.js will try to detect the syntax with the following steps:

1. Run the input as CommonJS.
2. If step 1 fails, run the input as an ES module.
3. If step 2 fails with a SyntaxError, strip the types.
4. If step 3 fails with an error code ERR_UNSUPPORTED_TYPESCRIPT_SYNTAX or ERR_INVALID_TYPESCRIPT_SYNTAX, throw the error from step 2, including the TypeScript error in the message, else run as CommonJS.
5. If step 4 fails, run the input as an ES module.

To avoid the delay of multiple syntax detection passes, the --input-type=type flag can be used to specify how the --eval input should be interpreted.

The REPL does not support this option. Usage of --input-type=module with --print will throw an error, as --print does not support ES module syntax.

--insecure-http-parser#

Enable leniency flags on the HTTP parser. This may allow interoperability with non-conformant HTTP implementations.

When enabled, the parser will accept the following:

• Invalid HTTP headers values.
• Invalid HTTP versions.
• Allow message containing both Transfer-Encoding and Content-Length headers.
• Allow extra data after message when Connection: close is present.
• Allow extra transfer encodings after chunked has been provided.
• Allow \n to be used as token separator instead of \r\n.
• Allow \r\n not to be provided after a chunk.
• Allow spaces to be present after a chunk size and before \r\n.

All the above will expose your application to request smuggling or poisoning attack. Avoid using this option.

--inspect-brk[=[host:]port]#

Activate inspector on host:port and break at start of user script. Default host:port is 127.0.0.1:9229. If port 0 is specified, a random available port will be used.

See V8 Inspector integration for Node.js for further explanation on Node.js debugger.

See the security warning below regarding the host parameter usage.

--inspect-port=[host:]port#

Set the host:port to be used when the inspector is activated. Useful when activating the inspector by sending the SIGUSR1 signal. Except when --disable-sigusr1 is passed.

Default host is 127.0.0.1. If port 0 is specified, a random available port will be used.

See the security warning below regarding the host parameter usage.

--inspect-publish-uid=stderr,http#

Specify ways of the inspector web socket url exposure.

By default inspector websocket url is available in stderr and under /json/list endpoint on http://host:port/json/list.

--inspect-wait[=[host:]port]#

Activate inspector on host:port and wait for debugger to be attached. Default host:port is 127.0.0.1:9229. If port 0 is specified, a random available port will be used.

See V8 Inspector integration for Node.js for further explanation on Node.js debugger.

See the security warning below regarding the host parameter usage.

--inspect[=[host:]port]#

Activate inspector on host:port. Default is 127.0.0.1:9229. If port 0 is specified, a random available port will be used.

V8 inspector integration allows tools such as Chrome DevTools and IDEs to debug and profile Node.js instances. The tools attach to Node.js instances via a tcp port and communicate using the Chrome DevTools Protocol. See V8 Inspector integration for Node.js for further explanation on Node.js debugger.

Warning: binding inspector to a public IP:port combination is insecure#

Binding the inspector to a public IP (including 0.0.0.0) with an open port is insecure, as it allows external hosts to connect to the inspector and perform a remote code execution attack.

If specifying a host, make sure that either:

• The host is not accessible from public networks.
• A firewall disallows unwanted connections on the port.

More specifically, --inspect=0.0.0.0 is insecure if the port (9229 by default) is not firewall-protected.

See the debugging security implications section for more information.

-i, --interactive#

Opens the REPL even if stdin does not appear to be a terminal.

--jitless#

Disable runtime allocation of executable memory. This may be required on some platforms for security reasons. It can also reduce attack surface on other platforms, but the performance impact may be severe.

--localstorage-file=file#

The file used to store localStorage data. If the file does not exist, it is created the first time localStorage is accessed. The same file may be shared between multiple Node.js processes concurrently.

--max-http-header-size=size#

Specify the maximum size, in bytes, of HTTP headers. Defaults to 16 KiB.

--max-old-space-size-percentage=percentage#

Sets the maximum memory size of V8's old memory section as a percentage of available system memory. This flag takes precedence over --max-old-space-size when both are specified.

The percentage parameter must be a number greater than 0 and up to 100, representing the percentage of available system memory to allocate to the V8 heap.

Note: This flag utilizes --max-old-space-size, which may be unreliable on 32-bit platforms due to integer overflow issues.

# Using 50% of available system memory
node --max-old-space-size-percentage=50 index.js

# Using 75% of available system memory
node --max-old-space-size-percentage=75 index.js
copy

--napi-modules#

This option is a no-op. It is kept for compatibility.

--network-family-autoselection-attempt-timeout#

Sets the default value for the network family autoselection attempt timeout. For more information, see net.getDefaultAutoSelectFamilyAttemptTimeout().

--no-addons#

Disable the node-addons exports condition as well as disable loading native addons. When --no-addons is specified, calling process.dlopen or requiring a native C++ addon will fail and throw an exception.

--no-async-context-frame#

Disables the use of AsyncLocalStorage backed by AsyncContextFrame and uses the prior implementation which relied on async_hooks. The previous model is retained for compatibility with Electron and for cases where the context flow may differ. However, if a difference in flow is found please report it.

--no-deprecation#

Silence deprecation warnings.

--no-experimental-detect-module#

Disable using syntax detection to determine module type.

--no-experimental-global-navigator#

Disable exposition of Navigator API on the global scope.

--no-experimental-repl-await#

Use this flag to disable top-level await in REPL.

--no-experimental-require-module#

Legacy alias for --no-require-module.

--no-experimental-sqlite#

Disable the experimental node:sqlite module.

--no-experimental-websocket#

Disable exposition of <WebSocket> on the global scope.

--no-experimental-webstorage#

Disable Web Storage support.

--no-extra-info-on-fatal-exception#

Hide extra information on fatal exception that causes exit.

--no-force-async-hooks-checks#

Disables runtime checks for async_hooks. These will still be enabled dynamically when async_hooks is enabled.

--no-global-search-paths#

Do not search modules from global paths like $HOME/.node_modules and $NODE_PATH.

--no-network-family-autoselection#

Disables the family autoselection algorithm unless connection options explicitly enables it.

--no-require-module#

Disable support for loading a synchronous ES module graph in require().

See Loading ECMAScript modules using require().

--no-strip-types#

Disable type-stripping for TypeScript files. For more information, see the TypeScript type-stripping documentation.

--no-warnings#

Silence all process warnings (including deprecations).

--node-memory-debug#

Enable extra debug checks for memory leaks in Node.js internals. This is usually only useful for developers debugging Node.js itself.

--openssl-config=file#

Load an OpenSSL configuration file on startup. Among other uses, this can be used to enable FIPS-compliant crypto if Node.js is built against FIPS-enabled OpenSSL.

--openssl-legacy-provider#

Enable OpenSSL 3.0 legacy provider. For more information please see OSSL_PROVIDER-legacy.

--openssl-shared-config#

Enable OpenSSL default configuration section, openssl_conf to be read from the OpenSSL configuration file. The default configuration file is named openssl.cnf but this can be changed using the environment variable OPENSSL_CONF, or by using the command line option --openssl-config. The location of the default OpenSSL configuration file depends on how OpenSSL is being linked to Node.js. Sharing the OpenSSL configuration may have unwanted implications and it is recommended to use a configuration section specific to Node.js which is nodejs_conf and is default when this option is not used.

--pending-deprecation#

Emit pending deprecation warnings.

Pending deprecations are generally identical to a runtime deprecation with the notable exception that they are turned off by default and will not be emitted unless either the --pending-deprecation command-line flag, or the NODE_PENDING_DEPRECATION=1 environment variable, is set. Pending deprecations are used to provide a kind of selective "early warning" mechanism that developers may leverage to detect deprecated API usage.

--permission#

Enable the Permission Model for current process. When enabled, the following permissions are restricted:

• File System - manageable through --allow-fs-read, --allow-fs-write flags
• Network - manageable through --allow-net flag
• Child Process - manageable through --allow-child-process flag
• Worker Threads - manageable through --allow-worker flag
• WASI - manageable through --allow-wasi flag
• Addons - manageable through --allow-addons flag

--permission-audit#

Enable audit only for the permission model. When enabled, permission checks are performed but access is not denied. Instead, a warning is emitted for each permission violation via diagnostics channel.

--preserve-symlinks#

Instructs the module loader to preserve symbolic links when resolving and caching modules.

By default, when Node.js loads a module from a path that is symbolically linked to a different on-disk location, Node.js will dereference the link and use the actual on-disk "real path" of the module as both an identifier and as a root path to locate other dependency modules. In most cases, this default behavior is acceptable. However, when using symbolically linked peer dependencies, as illustrated in the example below, the default behavior causes an exception to be thrown if moduleA attempts to require moduleB as a peer dependency:

{appDir}
 ├── app
 │   ├── index.js
 │   └── node_modules
 │       ├── moduleA -> {appDir}/moduleA
 │       └── moduleB
 │           ├── index.js
 │           └── package.json
 └── moduleA
     ├── index.js
     └── package.json
copy

The --preserve-symlinks command-line flag instructs Node.js to use the symlink path for modules as opposed to the real path, allowing symbolically linked peer dependencies to be found.

Note, however, that using --preserve-symlinks can have other side effects. Specifically, symbolically linked native modules can fail to load if those are linked from more than one location in the dependency tree (Node.js would see those as two separate modules and would attempt to load the module multiple times, causing an exception to be thrown).

The --preserve-symlinks flag does not apply to the main module, which allows node --preserve-symlinks node_module/.bin/<foo> to work. To apply the same behavior for the main module, also use --preserve-symlinks-main.

--preserve-symlinks-main#

Instructs the module loader to preserve symbolic links when resolving and caching the main module (require.main).

This flag exists so that the main module can be opted-in to the same behavior that --preserve-symlinks gives to all other imports; they are separate flags, however, for backward compatibility with older Node.js versions.

--preserve-symlinks-main does not imply --preserve-symlinks; use --preserve-symlinks-main in addition to --preserve-symlinks when it is not desirable to follow symlinks before resolving relative paths.

See --preserve-symlinks for more information.

-p, --print "script"#

Identical to -e but prints the result.

--prof#

Generate V8 profiler output.

--prof-process#

Process V8 profiler output generated using the V8 option --prof.

--redirect-warnings=file#

Write process warnings to the given file instead of printing to stderr. The file will be created if it does not exist, and will be appended to if it does. If an error occurs while attempting to write the warning to the file, the warning will be written to stderr instead.

The file name may be an absolute path. If it is not, the default directory it will be written to is controlled by the --diagnostic-dir command-line option.

--report-compact#

Write reports in a compact format, single-line JSON, more easily consumable by log processing systems than the default multi-line format designed for human consumption.

--report-dir=directory, --report-directory=directory#

Location at which the report will be generated.

--report-exclude-env#

When --report-exclude-env is passed the diagnostic report generated will not contain the environmentVariables data.

--report-exclude-network#

Exclude header.networkInterfaces from the diagnostic report. By default this is not set and the network interfaces are included.

--report-filename=filename#

Name of the file to which the report will be written.

If the filename is set to 'stdout' or 'stderr', the report is written to the stdout or stderr of the process respectively.

--report-on-fatalerror#

Enables the report to be triggered on fatal errors (internal errors within the Node.js runtime such as out of memory) that lead to termination of the application. Useful to inspect various diagnostic data elements such as heap, stack, event loop state, resource consumption etc. to reason about the fatal error.

--report-on-signal#

Enables report to be generated upon receiving the specified (or predefined) signal to the running Node.js process. The signal to trigger the report is specified through --report-signal.

--report-signal=signal#

Sets or resets the signal for report generation (not supported on Windows). Default signal is SIGUSR2.

--report-uncaught-exception#

Enables report to be generated when the process exits due to an uncaught exception. Useful when inspecting the JavaScript stack in conjunction with native stack and other runtime environment data.

-r, --require module#

Preload the specified module at startup.

Follows require()'s module resolution rules. module may be either a path to a file, or a node module name.

Modules preloaded with --require will run before modules preloaded with --import.

Modules are preloaded into the main thread as well as any worker threads, forked processes, or clustered processes.

--run#

This runs a specified command from a package.json's "scripts" object. If a missing "command" is provided, it will list the available scripts.

--run will traverse up to the root directory and finds a package.json file to run the command from.

--run prepends ./node_modules/.bin for each ancestor of the current directory, to the PATH in order to execute the binaries from different folders where multiple node_modules directories are present, if ancestor-folder/node_modules/.bin is a directory.

--run executes the command in the directory containing the related package.json.

For example, the following command will run the test script of the package.json in the current folder:

$ node --run test
copy

You can also pass arguments to the command. Any argument after -- will be appended to the script:

$ node --run test -- --verbose
copy

Intentional limitations#

node --run is not meant to match the behaviors of npm run or of the run commands of other package managers. The Node.js implementation is intentionally more limited, in order to focus on top performance for the most common use cases. Some features of other run implementations that are intentionally excluded are:

• Running pre or post scripts in addition to the specified script.
• Defining package manager-specific environment variables.

Environment variables#

The following environment variables are set when running a script with --run:

• NODE_RUN_SCRIPT_NAME: The name of the script being run. For example, if --run is used to run test, the value of this variable will be test.
• NODE_RUN_PACKAGE_JSON_PATH: The path to the package.json that is being processed.

--secure-heap-min=n#

When using --secure-heap, the --secure-heap-min flag specifies the minimum allocation from the secure heap. The minimum value is 2. The maximum value is the lesser of --secure-heap or 2147483647. The value given must be a power of two.

--secure-heap=n#

Initializes an OpenSSL secure heap of n bytes. When initialized, the secure heap is used for selected types of allocations within OpenSSL during key generation and other operations. This is useful, for instance, to prevent sensitive information from leaking due to pointer overruns or underruns.

The secure heap is a fixed size and cannot be resized at runtime so, if used, it is important to select a large enough heap to cover all application uses.

The heap size given must be a power of two. Any value less than 2 will disable the secure heap.

The secure heap is disabled by default.

The secure heap is not available on Windows.

See CRYPTO_secure_malloc_init for more details.

--snapshot-blob=path#

When used with --build-snapshot, --snapshot-blob specifies the path where the generated snapshot blob is written to. If not specified, the generated blob is written to snapshot.blob in the current working directory.

When used without --build-snapshot, --snapshot-blob specifies the path to the blob that is used to restore the application state.

When loading a snapshot, Node.js checks that:

1. The version, architecture, and platform of the running Node.js binary are exactly the same as that of the binary that generates the snapshot.
2. The V8 flags and CPU features are compatible with that of the binary that generates the snapshot.

If they don't match, Node.js refuses to load the snapshot and exits with status code 1.

--test#

Starts the Node.js command line test runner. This flag cannot be combined with --watch-path, --check, --eval, --interactive, or the inspector. See the documentation on running tests from the command line for more details.

--test-concurrency#

The maximum number of test files that the test runner CLI will execute concurrently. If --test-isolation is set to 'none', this flag is ignored and concurrency is one. Otherwise, concurrency defaults to os.availableParallelism() - 1.

--test-coverage-branches=threshold#

Require a minimum percent of covered branches. If code coverage does not reach the threshold specified, the process will exit with code 1.

--test-coverage-exclude#

Excludes specific files from code coverage using a glob pattern, which can match both absolute and relative file paths.

This option may be specified multiple times to exclude multiple glob patterns.

If both --test-coverage-exclude and --test-coverage-include are provided, files must meet both criteria to be included in the coverage report.

By default all the matching test files are excluded from the coverage report. Specifying this option will override the default behavior.

--test-coverage-functions=threshold#

Require a minimum percent of covered functions. If code coverage does not reach the threshold specified, the process will exit with code 1.

--test-coverage-include#

Includes specific files in code coverage using a glob pattern, which can match both absolute and relative file paths.

This option may be specified multiple times to include multiple glob patterns.

If both --test-coverage-exclude and --test-coverage-include are provided, files must meet both criteria to be included in the coverage report.

--test-coverage-lines=threshold#

Require a minimum percent of covered lines. If code coverage does not reach the threshold specified, the process will exit with code 1.

--test-force-exit#

Configures the test runner to exit the process once all known tests have finished executing even if the event loop would otherwise remain active.

--test-global-setup=module#

Specify a module that will be evaluated before all tests are executed and can be used to setup global state or fixtures for tests.

See the documentation on global setup and teardown for more details.

--test-isolation=mode#

Configures the type of test isolation used in the test runner. When mode is 'process', each test file is run in a separate child process. When mode is 'none', all test files run in the same process as the test runner. The default isolation mode is 'process'. This flag is ignored if the --test flag is not present. See the test runner execution model section for more information.

--test-name-pattern#

A regular expression that configures the test runner to only execute tests whose name matches the provided pattern. See the documentation on filtering tests by name for more details.

If both --test-name-pattern and --test-skip-pattern are supplied, tests must satisfy both requirements in order to be executed.

--test-only#

Configures the test runner to only execute top level tests that have the only option set. This flag is not necessary when test isolation is disabled.

--test-reporter#

A test reporter to use when running tests. See the documentation on test reporters for more details.

--test-reporter-destination#

The destination for the corresponding test reporter. See the documentation on test reporters for more details.

--test-rerun-failures#

A path to a file allowing the test runner to persist the state of the test suite between runs. The test runner will use this file to determine which tests have already succeeded or failed, allowing for re-running of failed tests without having to re-run the entire test suite. The test runner will create this file if it does not exist. See the documentation on test reruns for more details.

--test-shard#

Test suite shard to execute in a format of <index>/<total>, where

• index is a positive integer, index of divided parts.
• total is a positive integer, total of divided part.

This command will divide all tests files into total equal parts, and will run only those that happen to be in an index part.

For example, to split your tests suite into three parts, use this:

node --test --test-shard=1/3
node --test --test-shard=2/3
node --test --test-shard=3/3
copy

--test-skip-pattern#

A regular expression that configures the test runner to skip tests whose name matches the provided pattern. See the documentation on filtering tests by name for more details.

If both --test-name-pattern and --test-skip-pattern are supplied, tests must satisfy both requirements in order to be executed.

--test-timeout#

A number of milliseconds the test execution will fail after. If unspecified, subtests inherit this value from their parent. The default value is Infinity.

--test-update-snapshots#

Regenerates the snapshot files used by the test runner for snapshot testing.

--throw-deprecation#

Throw errors for deprecations.

--title=title#

Set process.title on startup.

--tls-cipher-list=list#

Specify an alternative default TLS cipher list. Requires Node.js to be built with crypto support (default).

--tls-keylog=file#

Log TLS key material to a file. The key material is in NSS SSLKEYLOGFILE format and can be used by software (such as Wireshark) to decrypt the TLS traffic.

--tls-max-v1.2#

Set tls.DEFAULT_MAX_VERSION to 'TLSv1.2'. Use to disable support for TLSv1.3.

--tls-max-v1.3#

Set default tls.DEFAULT_MAX_VERSION to 'TLSv1.3'. Use to enable support for TLSv1.3.

--tls-min-v1.0#

Set default tls.DEFAULT_MIN_VERSION to 'TLSv1'. Use for compatibility with old TLS clients or servers.

--tls-min-v1.1#

Set default tls.DEFAULT_MIN_VERSION to 'TLSv1.1'. Use for compatibility with old TLS clients or servers.

--tls-min-v1.2#

Set default tls.DEFAULT_MIN_VERSION to 'TLSv1.2'. This is the default for 12.x and later, but the option is supported for compatibility with older Node.js versions.

--tls-min-v1.3#

Set default tls.DEFAULT_MIN_VERSION to 'TLSv1.3'. Use to disable support for TLSv1.2, which is not as secure as TLSv1.3.

--trace-deprecation#

Print stack traces for deprecations.

--trace-env#

Print information about any access to environment variables done in the current Node.js instance to stderr, including:

• The environment variable reads that Node.js does internally.
• Writes in the form of process.env.KEY = "SOME VALUE".
• Reads in the form of process.env.KEY.
• Definitions in the form of Object.defineProperty(process.env, 'KEY', {...}).
• Queries in the form of Object.hasOwn(process.env, 'KEY'), process.env.hasOwnProperty('KEY') or 'KEY' in process.env.
• Deletions in the form of delete process.env.KEY.
• Enumerations inf the form of ...process.env or Object.keys(process.env).

Only the names of the environment variables being accessed are printed. The values are not printed.

To print the stack trace of the access, use --trace-env-js-stack and/or --trace-env-native-stack.

--trace-env-js-stack#

In addition to what --trace-env does, this prints the JavaScript stack trace of the access.

--trace-env-native-stack#

In addition to what --trace-env does, this prints the native stack trace of the access.

--trace-event-categories#

A comma separated list of categories that should be traced when trace event tracing is enabled using --trace-events-enabled.

--trace-event-file-pattern#

Template string specifying the filepath for the trace event data, it supports ${rotation} and ${pid}.

--trace-events-enabled#

Enables the collection of trace event tracing information.

--trace-exit#

Prints a stack trace whenever an environment is exited proactively, i.e. invoking process.exit().

--trace-require-module=mode#

Prints information about usage of Loading ECMAScript modules using require().

When mode is all, all usage is printed. When mode is no-node-modules, usage from the node_modules folder is excluded.

--trace-sigint#

Prints a stack trace on SIGINT.

--trace-sync-io#

Prints a stack trace whenever synchronous I/O is detected after the first turn of the event loop.

--trace-tls#

Prints TLS packet trace information to stderr. This can be used to debug TLS connection problems.

--trace-uncaught#

Print stack traces for uncaught exceptions; usually, the stack trace associated with the creation of an Error is printed, whereas this makes Node.js also print the stack trace associated with throwing the value (which does not need to be an Error instance).

Enabling this option may affect garbage collection behavior negatively.

--trace-warnings#

Print stack traces for process warnings (including deprecations).

--track-heap-objects#

Track heap object allocations for heap snapshots.

--unhandled-rejections=mode#

Using this flag allows to change what should happen when an unhandled rejection occurs. One of the following modes can be chosen:

• throw: Emit unhandledRejection. If this hook is not set, raise the unhandled rejection as an uncaught exception. This is the default.
• strict: Raise the unhandled rejection as an uncaught exception. If the exception is handled, unhandledRejection is emitted.
• warn: Always trigger a warning, no matter if the unhandledRejection hook is set or not but do not print the deprecation warning.
• warn-with-error-code: Emit unhandledRejection. If this hook is not set, trigger a warning, and set the process exit code to 1.
• none: Silence all warnings.

If a rejection happens during the command line entry point's ES module static loading phase, it will always raise it as an uncaught exception.

--use-bundled-ca, --use-openssl-ca#

Use bundled Mozilla CA store as supplied by current Node.js version or use OpenSSL's default CA store. The default store is selectable at build-time.

The bundled CA store, as supplied by Node.js, is a snapshot of Mozilla CA store that is fixed at release time. It is identical on all supported platforms.

Using OpenSSL store allows for external modifications of the store. For most Linux and BSD distributions, this store is maintained by the distribution maintainers and system administrators. OpenSSL CA store location is dependent on configuration of the OpenSSL library but this can be altered at runtime using environment variables.

See SSL_CERT_DIR and SSL_CERT_FILE.

--use-env-proxy#

When enabled, Node.js parses the HTTP_PROXY, HTTPS_PROXY and NO_PROXY environment variables during startup, and tunnels requests over the specified proxy.

This is equivalent to setting the NODE_USE_ENV_PROXY=1 environment variable. When both are set, --use-env-proxy takes precedence.

--use-largepages=mode#

Re-map the Node.js static code to large memory pages at startup. If supported on the target system, this will cause the Node.js static code to be moved onto 2 MiB pages instead of 4 KiB pages.

The following values are valid for mode:

• off: No mapping will be attempted. This is the default.
• on: If supported by the OS, mapping will be attempted. Failure to map will be ignored and a message will be printed to standard error.
• silent: If supported by the OS, mapping will be attempted. Failure to map will be ignored and will not be reported.

--use-system-ca#

Node.js uses the trusted CA certificates present in the system store along with the --use-bundled-ca option and the NODE_EXTRA_CA_CERTS environment variable. On platforms other than Windows and macOS, this loads certificates from the directory and file trusted by OpenSSL, similar to --use-openssl-ca, with the difference being that it caches the certificates after first load.

On Windows and macOS, the certificate trust policy is similar to Chromium's policy for locally trusted certificates, but with some differences:

On macOS, the following settings are respected:

• Default and System Keychains
  • Trust:
    • Any certificate where the “When using this certificate” flag is set to “Always Trust” or
    • Any certificate where the “Secure Sockets Layer (SSL)” flag is set to “Always Trust”.
  • The certificate must also be valid, with "X.509 Basic Policy" set to “Always Trust”.

On Windows, the following settings are respected:

• Local Machine (accessed via certlm.msc)
  • Trust:
    • Trusted Root Certification Authorities
    • Trusted People
    • Enterprise Trust -> Enterprise -> Trusted Root Certification Authorities
    • Enterprise Trust -> Enterprise -> Trusted People
    • Enterprise Trust -> Group Policy -> Trusted Root Certification Authorities
    • Enterprise Trust -> Group Policy -> Trusted People
• Current User (accessed via certmgr.msc)
  • Trust:
    • Trusted Root Certification Authorities
    • Enterprise Trust -> Group Policy -> Trusted Root Certification Authorities

On Windows and macOS, Node.js would check that the user settings for the trusted certificates do not forbid them for TLS server authentication before using them.

Node.js currently does not support distrust/revocation of certificates from another source based on system settings.

On other systems, Node.js loads certificates from the default certificate file (typically /etc/ssl/cert.pem) and default certificate directory (typically /etc/ssl/certs) that the version of OpenSSL that Node.js links to respects. This typically works with the convention on major Linux distributions and other Unix-like systems. If the overriding OpenSSL environment variables (typically SSL_CERT_FILE and SSL_CERT_DIR, depending on the configuration of the OpenSSL that Node.js links to) are set, the specified paths will be used to load certificates instead. These environment variables can be used as workarounds if the conventional paths used by the version of OpenSSL Node.js links to are not consistent with the system configuration that the users have for some reason.

--v8-options#

Print V8 command-line options.

--v8-pool-size=num#

Set V8's thread pool size which will be used to allocate background jobs.

If set to 0 then Node.js will choose an appropriate size of the thread pool based on an estimate of the amount of parallelism.

The amount of parallelism refers to the number of computations that can be carried out simultaneously in a given machine. In general, it's the same as the amount of CPUs, but it may diverge in environments such as VMs or containers.

-v, --version#

Print node's version.

--watch#

Starts Node.js in watch mode. When in watch mode, changes in the watched files cause the Node.js process to restart. By default, watch mode will watch the entry point and any required or imported module. Use --watch-path to specify what paths to watch.

This flag cannot be combined with --check, --eval, --interactive, or the REPL.

Note: The --watch flag requires a file path as an argument and is incompatible with --run or inline script input, as --run takes precedence and ignores watch mode. If no file is provided, Node.js will exit with status code 9.

node --watch index.js
copy

--watch-kill-signal#

Customizes the signal sent to the process on watch mode restarts.

node --watch --watch-kill-signal SIGINT test.js
copy

--watch-path#

Starts Node.js in watch mode and specifies what paths to watch. When in watch mode, changes in the watched paths cause the Node.js process to restart. This will turn off watching of required or imported modules, even when used in combination with --watch.

This flag cannot be combined with --check, --eval, --interactive, --test, or the REPL.

Note: Using --watch-path implicitly enables --watch, which requires a file path and is incompatible with --run, as --run takes precedence and ignores watch mode.

node --watch-path=./src --watch-path=./tests index.js
copy

This option is only supported on macOS and Windows. An ERR_FEATURE_UNAVAILABLE_ON_PLATFORM exception will be thrown when the option is used on a platform that does not support it.

--watch-preserve-output#

Disable the clearing of the console when watch mode restarts the process.

node --watch --watch-preserve-output test.js
copy

--zero-fill-buffers#

Automatically zero-fills all newly allocated Buffer instances.

Environment variables#

FORCE_COLOR=[1, 2, 3]#

The FORCE_COLOR environment variable is used to enable ANSI colorized output. The value may be:

• 1, true, or the empty string '' indicate 16-color support,
• 2 to indicate 256-color support, or
• 3 to indicate 16 million-color support.

When FORCE_COLOR is used and set to a supported value, both the NO_COLOR, and NODE_DISABLE_COLORS environment variables are ignored.

Any other value will result in colorized output being disabled.

NODE_COMPILE_CACHE=dir#

Enable the module compile cache for the Node.js instance. See the documentation of module compile cache for details.

NODE_COMPILE_CACHE_PORTABLE=1#

When set to 1, the module compile cache can be reused across different directory locations as long as the module layout relative to the cache directory remains the same.

NODE_DEBUG=module[,…]#

','-separated list of core modules that should print debug information.

NODE_DEBUG_NATIVE=module[,…]#

','-separated list of core C++ modules that should print debug information.

NODE_DISABLE_COLORS=1#

When set, colors will not be used in the REPL.

NODE_DISABLE_COMPILE_CACHE=1#

Disable the module compile cache for the Node.js instance. See the documentation of module compile cache for details.

NODE_EXTRA_CA_CERTS=file#

When set, the well known "root" CAs (like VeriSign) will be extended with the extra certificates in file. The file should consist of one or more trusted certificates in PEM format. A message will be emitted (once) with process.emitWarning() if the file is missing or malformed, but any errors are otherwise ignored.

Neither the well known nor extra certificates are used when the ca options property is explicitly specified for a TLS or HTTPS client or server.

This environment variable is ignored when node runs as setuid root or has Linux file capabilities set.

The NODE_EXTRA_CA_CERTS environment variable is only read when the Node.js process is first launched. Changing the value at runtime using process.env.NODE_EXTRA_CA_CERTS has no effect on the current process.

NODE_ICU_DATA=file#

Data path for ICU (Intl object) data. Will extend linked-in data when compiled with small-icu support.

NODE_NO_WARNINGS=1#

When set to 1, process warnings are silenced.

NODE_OPTIONS=options...#

A space-separated list of command-line options. options... are interpreted before command-line options, so command-line options will override or compound after anything in options.... Node.js will exit with an error if an option that is not allowed in the environment is used, such as -p or a script file.

If an option value contains a space, it can be escaped using double quotes:

NODE_OPTIONS='--require "./my path/file.js"'
copy

A singleton flag passed as a command-line option will override the same flag passed into NODE_OPTIONS:

# The inspector will be available on port 5555
NODE_OPTIONS='--inspect=localhost:4444' node --inspect=localhost:5555
copy

A flag that can be passed multiple times will be treated as if its NODE_OPTIONS instances were passed first, and then its command-line instances afterwards:

NODE_OPTIONS='--require "./a.js"' node --require "./b.js"
# is equivalent to:
node --require "./a.js" --require "./b.js"
copy

Node.js options that are allowed are in the following list. If an option supports both --XX and --no-XX variants, they are both supported but only one is included in the list below.

• --allow-addons
• --allow-child-process
• --allow-fs-read
• --allow-fs-write
• --allow-inspector
• --allow-net
• --allow-wasi
• --allow-worker
• --conditions, -C
• --cpu-prof-dir
• --cpu-prof-interval
• --cpu-prof-name
• --cpu-prof
• --diagnostic-dir
• --disable-proto
• --disable-sigusr1
• --disable-warning
• --disable-wasm-trap-handler
• --dns-result-order
• --enable-fips
• --enable-network-family-autoselection
• --enable-source-maps
• --entry-url
• --experimental-abortcontroller
• --experimental-addon-modules
• --experimental-detect-module
• --experimental-eventsource
• --experimental-import-meta-resolve
• --experimental-json-modules
• --experimental-loader
• --experimental-modules
• --experimental-print-required-tla
• --experimental-quic
• --experimental-require-module
• --experimental-shadow-realm
• --experimental-specifier-resolution
• --experimental-test-isolation
• --experimental-top-level-await
• --experimental-transform-types
• --experimental-vm-modules
• --experimental-wasi-unstable-preview1
• --force-context-aware
• --force-fips
• --force-node-api-uncaught-exceptions-policy
• --frozen-intrinsics
• --heap-prof-dir
• --heap-prof-interval
• --heap-prof-name
• --heap-prof
• --heapsnapshot-near-heap-limit
• --heapsnapshot-signal
• --http-parser
• --icu-data-dir
• --import
• --input-type
• --insecure-http-parser
• --inspect-brk
• --inspect-port, --debug-port
• --inspect-publish-uid
• --inspect-wait
• --inspect
• --localstorage-file
• --max-http-header-size
• --max-old-space-size-percentage
• --napi-modules
• --network-family-autoselection-attempt-timeout
• --no-addons
• --no-async-context-frame
• --no-deprecation
• --no-experimental-global-navigator
• --no-experimental-repl-await
• --no-experimental-sqlite
• --no-experimental-strip-types
• --no-experimental-websocket
• --no-experimental-webstorage
• --no-extra-info-on-fatal-exception
• --no-force-async-hooks-checks
• --no-global-search-paths
• --no-network-family-autoselection
• --no-strip-types
• --no-warnings
• --no-webstorage
• --node-memory-debug
• --openssl-config
• --openssl-legacy-provider
• --openssl-shared-config
• --pending-deprecation
• --permission-audit
• --permission
• --preserve-symlinks-main
• --preserve-symlinks
• --prof-process
• --redirect-warnings
• --report-compact
• --report-dir, --report-directory
• --report-exclude-env
• --report-exclude-network
• --report-filename
• --report-on-fatalerror
• --report-on-signal
• --report-signal
• --report-uncaught-exception
• --require-module
• --require, -r
• --secure-heap-min
• --secure-heap
• --snapshot-blob
• --test-coverage-branches
• --test-coverage-exclude
• --test-coverage-functions
• --test-coverage-include
• --test-coverage-lines
• --test-global-setup
• --test-isolation
• --test-name-pattern
• --test-only
• --test-reporter-destination
• --test-reporter
• --test-rerun-failures
• --test-shard
• --test-skip-pattern
• --throw-deprecation
• --title
• --tls-cipher-list
• --tls-keylog
• --tls-max-v1.2
• --tls-max-v1.3
• --tls-min-v1.0
• --tls-min-v1.1
• --tls-min-v1.2
• --tls-min-v1.3
• --trace-deprecation
• --trace-env-js-stack
• --trace-env-native-stack
• --trace-env
• --trace-event-categories
• --trace-event-file-pattern
• --trace-events-enabled
• --trace-exit
• --trace-require-module
• --trace-sigint
• --trace-sync-io
• --trace-tls
• --trace-uncaught
• --trace-warnings
• --track-heap-objects
• --unhandled-rejections
• --use-bundled-ca
• --use-env-proxy
• --use-largepages
• --use-openssl-ca
• --use-system-ca
• --v8-pool-size
• --watch-kill-signal
• --watch-path
• --watch-preserve-output
• --watch
• --zero-fill-buffers

V8 options that are allowed are:

• --abort-on-uncaught-exception
• --disallow-code-generation-from-strings
• --enable-etw-stack-walking
• --expose-gc
• --interpreted-frames-native-stack
• --jitless
• --max-old-space-size
• --max-semi-space-size
• --perf-basic-prof-only-functions
• --perf-basic-prof
• --perf-prof-unwinding-info
• --perf-prof
• --stack-trace-limit

--perf-basic-prof-only-functions, --perf-basic-prof, --perf-prof-unwinding-info, and --perf-prof are only available on Linux.

--enable-etw-stack-walking is only available on Windows.

NODE_PATH=path[:…]#

':'-separated list of directories prefixed to the module search path.

On Windows, this is a ';'-separated list instead.

NODE_PENDING_DEPRECATION=1#

When set to 1, emit pending deprecation warnings.

Pending deprecations are generally identical to a runtime deprecation with the notable exception that they are turned off by default and will not be emitted unless either the --pending-deprecation command-line flag, or the NODE_PENDING_DEPRECATION=1 environment variable, is set. Pending deprecations are used to provide a kind of selective "early warning" mechanism that developers may leverage to detect deprecated API usage.

NODE_PENDING_PIPE_INSTANCES=instances#

Set the number of pending pipe instance handles when the pipe server is waiting for connections. This setting applies to Windows only.

NODE_PRESERVE_SYMLINKS=1#

When set to 1, instructs the module loader to preserve symbolic links when resolving and caching modules.

NODE_REDIRECT_WARNINGS=file#

When set, process warnings will be emitted to the given file instead of printing to stderr. The file will be created if it does not exist, and will be appended to if it does. If an error occurs while attempting to write the warning to the file, the warning will be written to stderr instead. This is equivalent to using the --redirect-warnings=file command-line flag.

NODE_REPL_EXTERNAL_MODULE=file#

Path to a Node.js module which will be loaded in place of the built-in REPL. Overriding this value to an empty string ('') will use the built-in REPL.

NODE_REPL_HISTORY=file#

Path to the file used to store the persistent REPL history. The default path is ~/.node_repl_history, which is overridden by this variable. Setting the value to an empty string ('' or ' ') disables persistent REPL history.

NODE_SKIP_PLATFORM_CHECK=value#

If value equals '1', the check for a supported platform is skipped during Node.js startup. Node.js might not execute correctly. Any issues encountered on unsupported platforms will not be fixed.

NODE_TEST_CONTEXT=value#

If value equals 'child', test reporter options will be overridden and test output will be sent to stdout in the TAP format. If any other value is provided, Node.js makes no guarantees about the reporter format used or its stability.

NODE_TLS_REJECT_UNAUTHORIZED=value#

If value equals '0', certificate validation is disabled for TLS connections. This makes TLS, and HTTPS by extension, insecure. The use of this environment variable is strongly discouraged.

NODE_USE_ENV_PROXY=1#

When enabled, Node.js parses the HTTP_PROXY, HTTPS_PROXY and NO_PROXY environment variables during startup, and tunnels requests over the specified proxy.

This can also be enabled using the --use-env-proxy command-line flag. When both are set, --use-env-proxy takes precedence.

NODE_USE_SYSTEM_CA=1#

Node.js uses the trusted CA certificates present in the system store along with the --use-bundled-ca option and the NODE_EXTRA_CA_CERTS environment variable.

This can also be enabled using the --use-system-ca command-line flag. When both are set, --use-system-ca takes precedence.

NODE_V8_COVERAGE=dir#

When set, Node.js will begin outputting V8 JavaScript code coverage and Source Map data to the directory provided as an argument (coverage information is written as JSON to files with a coverage prefix).

NODE_V8_COVERAGE will automatically propagate to subprocesses, making it easier to instrument applications that call the child_process.spawn() family of functions. NODE_V8_COVERAGE can be set to an empty string, to prevent propagation.

Coverage output#

Coverage is output as an array of ScriptCoverage objects on the top-level key result:

{
  "result": [
    {
      "scriptId": "67",
      "url": "internal/tty.js",
      "functions": []
    }
  ]
}
copy

Source map cache#

If found, source map data is appended to the top-level key source-map-cache on the JSON coverage object.

source-map-cache is an object with keys representing the files source maps were extracted from, and values which include the raw source-map URL (in the key url), the parsed Source Map v3 information (in the key data), and the line lengths of the source file (in the key lineLengths).

{
  "result": [
    {
      "scriptId": "68",
      "url": "file:///absolute/path/to/source.js",
      "functions": []
    }
  ],
  "source-map-cache": {
    "file:///absolute/path/to/source.js": {
      "url": "./path-to-map.json",
      "data": {
        "version": 3,
        "sources": [
          "file:///absolute/path/to/original.js"
        ],
        "names": [
          "Foo",
          "console",
          "info"
        ],
        "mappings": "MAAMA,IACJC,YAAaC",
        "sourceRoot": "./"
      },
      "lineLengths": [
        13,
        62,
        38,
        27
      ]
    }
  }
}
copy

NO_COLOR=<any>#

NO_COLOR is an alias for NODE_DISABLE_COLORS. The value of the environment variable is arbitrary.

OPENSSL_CONF=file#

Load an OpenSSL configuration file on startup. Among other uses, this can be used to enable FIPS-compliant crypto if Node.js is built with ./configure --openssl-fips.

If the --openssl-config command-line option is used, the environment variable is ignored.

SSL_CERT_DIR=dir#

If --use-openssl-ca is enabled, or if --use-system-ca is enabled on platforms other than macOS and Windows, this overrides and sets OpenSSL's directory containing trusted certificates.

Be aware that unless the child environment is explicitly set, this environment variable will be inherited by any child processes, and if they use OpenSSL, it may cause them to trust the same CAs as node.

SSL_CERT_FILE=file#

If --use-openssl-ca is enabled, or if --use-system-ca is enabled on platforms other than macOS and Windows, this overrides and sets OpenSSL's file containing trusted certificates.

Be aware that unless the child environment is explicitly set, this environment variable will be inherited by any child processes, and if they use OpenSSL, it may cause them to trust the same CAs as node.

TZ#

The TZ environment variable is used to specify the timezone configuration.

While Node.js does not support all of the various ways that TZ is handled in other environments, it does support basic timezone IDs (such as 'Etc/UTC', 'Europe/Paris', or 'America/New_York'). It may support a few other abbreviations or aliases, but these are strongly discouraged and not guaranteed.

$ TZ=Europe/Dublin node -pe "new Date().toString()"
Wed May 12 2021 20:30:48 GMT+0100 (Irish Standard Time)
copy

UV_THREADPOOL_SIZE=size#

Set the number of threads used in libuv's threadpool to size threads.

Asynchronous system APIs are used by Node.js whenever possible, but where they do not exist, libuv's threadpool is used to create asynchronous node APIs based on synchronous system APIs. Node.js APIs that use the threadpool are:

• all fs APIs, other than the file watcher APIs and those that are explicitly synchronous
• asynchronous crypto APIs such as crypto.pbkdf2(), crypto.scrypt(), crypto.randomBytes(), crypto.randomFill(), crypto.generateKeyPair()
• dns.lookup()
• all zlib APIs, other than those that are explicitly synchronous

Because libuv's threadpool has a fixed size, it means that if for whatever reason any of these APIs takes a long time, other (seemingly unrelated) APIs that run in libuv's threadpool will experience degraded performance. In order to mitigate this issue, one potential solution is to increase the size of libuv's threadpool by setting the 'UV_THREADPOOL_SIZE' environment variable to a value greater than 4 (its current default value). However, setting this from inside the process using process.env.UV_THREADPOOL_SIZE=size is not guranteed to work as the threadpool would have been created as part of the runtime initialisation much before user code is run. For more information, see the libuv threadpool documentation.

Useful V8 options#

V8 has its own set of CLI options. Any V8 CLI option that is provided to node will be passed on to V8 to handle. V8's options have no stability guarantee. The V8 team themselves don't consider them to be part of their formal API, and reserve the right to change them at any time. Likewise, they are not covered by the Node.js stability guarantees. Many of the V8 options are of interest only to V8 developers. Despite this, there is a small set of V8 options that are widely applicable to Node.js, and they are documented here:

--abort-on-uncaught-exception#

--disallow-code-generation-from-strings#

--enable-etw-stack-walking#

--expose-gc#

--harmony-shadow-realm#

--heap-snapshot-on-oom#

--interpreted-frames-native-stack#

--jitless#

--max-old-space-size=SIZE (in MiB)#

Sets the max memory size of V8's old memory section. As memory consumption approaches the limit, V8 will spend more time on garbage collection in an effort to free unused memory.

On a machine with 2 GiB of memory, consider setting this to 1536 (1.5 GiB) to leave some memory for other uses and avoid swapping.

node --max-old-space-size=1536 index.js
copy

--max-semi-space-size=SIZE (in MiB)#

Sets the maximum semi-space size for V8's scavenge garbage collector in MiB (mebibytes). Increasing the max size of a semi-space may improve throughput for Node.js at the cost of more memory consumption.

Since the young generation size of the V8 heap is three times (see YoungGenerationSizeFromSemiSpaceSize in V8) the size of the semi-space, an increase of 1 MiB to semi-space applies to each of the three individual semi-spaces and causes the heap size to increase by 3 MiB. The throughput improvement depends on your workload (see #42511).

The default value depends on the memory limit. For example, on 64-bit systems with a memory limit of 512 MiB, the max size of a semi-space defaults to 1 MiB. For memory limits up to and including 2GiB, the default max size of a semi-space will be less than 16 MiB on 64-bit systems.

To get the best configuration for your application, you should try different max-semi-space-size values when running benchmarks for your application.

For example, benchmark on a 64-bit systems:

for MiB in 16 32 64 128; do
    node --max-semi-space-size=$MiB index.js
done
copy

--perf-basic-prof#

--perf-basic-prof-only-functions#

--perf-prof#

--perf-prof-unwinding-info#

--prof#

--security-revert#

--stack-trace-limit=limit#

The maximum number of stack frames to collect in an error's stack trace. Setting it to 0 disables stack trace collection. The default value is 10.

node --stack-trace-limit=12 -p -e "Error.stackTraceLimit" # prints 12
copy

Console#

The node:console module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers.

The module exports two specific components:

• A Console class with methods such as console.log(), console.error(), and console.warn() that can be used to write to any Node.js stream.
• A global console instance configured to write to process.stdout and process.stderr. The global console can be used without calling require('node:console').

Warning: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. Programs that desire to depend on the synchronous / asynchronous behavior of the console functions should first figure out the nature of console's backing stream. This is because the stream is dependent on the underlying platform and standard stream configuration of the current process. See the note on process I/O for more information.

Example using the global console:

console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(new Error('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
//   Error: Whoops, something bad happened
//     at [eval]:5:15
//     at Script.runInThisContext (node:vm:132:18)
//     at Object.runInThisContext (node:vm:309:38)
//     at node:internal/process/execution:77:19
//     at [eval]-wrapper:6:22
//     at evalScript (node:internal/process/execution:76:60)
//     at node:internal/main/eval_string:23:3

const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
copy

Example using the Console class:

const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = new console.Console(out, err);

myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err

const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
copy

Class: Console#

The Console class can be used to create a simple logger with configurable output streams and can be accessed using either require('node:console').Console or console.Console (or their destructured counterparts):

import { Console } from 'node:console';
const { Console } = require('node:console');
copy

const { Console } = console;
copy

new Console(stdout[, stderr][, ignoreErrors])#

new Console(options)#

• options <Object>
  • stdout <stream.Writable>
  • stderr <stream.Writable>
  • ignoreErrors <boolean> Ignore errors when writing to the underlying streams. Default: true.
  • colorMode <boolean> | <string> Set color support for this Console instance. Setting to true enables coloring while inspecting values. Setting to false disables coloring while inspecting values. Setting to 'auto' makes color support depend on the value of the isTTY property and the value returned by getColorDepth() on the respective stream. This option can not be used, if inspectOptions.colors is set as well. Default: 'auto'.
  • inspectOptions <Object> | <Map> Specifies options that are passed along to util.inspect(). Can be an options object or, if different options for stdout and stderr are desired, a Map from stream objects to options.
  • groupIndentation <number> Set group indentation. Default: 2.

Creates a new Console with one or two writable stream instances. stdout is a writable stream to print log or info output. stderr is used for warning or error output. If stderr is not provided, stdout is used for stderr.

import { createWriteStream } from 'node:fs';
import { Console } from 'node:console';
// Alternatively
// const { Console } = console;

const output = createWriteStream('./stdout.log');
const errorOutput = createWriteStream('./stderr.log');
// Custom simple logger
const logger = new Console({ stdout: output, stderr: errorOutput });
// use it like console
const count = 5;
logger.log('count: %d', count);
// In stdout.log: count 5
const fs = require('node:fs');
const { Console } = require('node:console');
// Alternatively
// const { Console } = console;

const output = fs.createWriteStream('./stdout.log');
const errorOutput = fs.createWriteStream('./stderr.log');
// Custom simple logger
const logger = new Console({ stdout: output, stderr: errorOutput });
// use it like console
const count = 5;
logger.log('count: %d', count);
// In stdout.log: count 5
copy

The global console is a special Console whose output is sent to process.stdout and process.stderr. It is equivalent to calling:

new Console({ stdout: process.stdout, stderr: process.stderr });
copy

console.assert(value[, ...message])#

• value <any> The value tested for being truthy.
• ...message <any> All arguments besides value are used as error message.

console.assert() writes a message if value is falsy or omitted. It only writes a message and does not otherwise affect execution. The output always starts with "Assertion failed". If provided, message is formatted using util.format().

If value is truthy, nothing happens.

console.assert(true, 'does nothing');

console.assert(false, 'Whoops %s work', 'didn\'t');
// Assertion failed: Whoops didn't work

console.assert();
// Assertion failed
copy

console.clear()#

When stdout is a TTY, calling console.clear() will attempt to clear the TTY. When stdout is not a TTY, this method does nothing.

The specific operation of console.clear() can vary across operating systems and terminal types. For most Linux operating systems, console.clear() operates similarly to the clear shell command. On Windows, console.clear() will clear only the output in the current terminal viewport for the Node.js binary.

console.count([label])#

• label <string> The display label for the counter. Default: 'default'.

Maintains an internal counter specific to label and outputs to stdout the number of times console.count() has been called with the given label.

> console.count()
default: 1
undefined
> console.count('default')
default: 2
undefined
> console.count('abc')
abc: 1
undefined
> console.count('xyz')
xyz: 1
undefined
> console.count('abc')
abc: 2
undefined
> console.count()
default: 3
undefined
>
copy

console.countReset([label])#

• label <string> The display label for the counter. Default: 'default'.

Resets the internal counter specific to label.

> console.count('abc');
abc: 1
undefined
> console.countReset('abc');
undefined
> console.count('abc');
abc: 1
undefined
>
copy

console.debug(data[, ...args])#

• data <any>
• ...args <any>

The console.debug() function is an alias for console.log().

console.dir(obj[, options])#

• obj <any>
• options <Object>
  • showHidden <boolean> If true then the object's non-enumerable and symbol properties will be shown too. Default: false.
  • depth <number> Tells util.inspect() how many times to recurse while formatting the object. This is useful for inspecting large complicated objects. To make it recurse indefinitely, pass null. Default: 2.
  • colors <boolean> If true, then the output will be styled with ANSI color codes. Colors are customizable; see customizing util.inspect() colors. Default: false.

Uses util.inspect() on obj and prints the resulting string to stdout. This function bypasses any custom inspect() function defined on obj.

console.dirxml(...data)#

• ...data <any>

This method calls console.log() passing it the arguments received. This method does not produce any XML formatting.

console.error([data][, ...args])#

• data <any>
• ...args <any>

Prints to stderr with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to printf(3) (the arguments are all passed to util.format()).

const code = 5;
console.error('error #%d', code);
// Prints: error #5, to stderr
console.error('error', code);
// Prints: error 5, to stderr
copy

If formatting elements (e.g. %d) are not found in the first string then util.inspect() is called on each argument and the resulting string values are concatenated. See util.format() for more information.

console.group([...label])#

• ...label <any>

Increases indentation of subsequent lines by spaces for groupIndentation length.

If one or more labels are provided, those are printed first without the additional indentation.

console.groupCollapsed()#

An alias for console.group().

console.groupEnd()#

Decreases indentation of subsequent lines by spaces for groupIndentation length.

console.info([data][, ...args])#

• data <any>
• ...args <any>

The console.info() function is an alias for console.log().

console.log([data][, ...args])#

• data <any>
• ...args <any>

Prints to stdout with newline. Multiple arguments can be passed, with the first used as the primary message and all additional used as substitution values similar to printf(3) (the arguments are all passed to util.format()).

const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout
copy

See util.format() for more information.

console.table(tabularData[, properties])#

• tabularData <any>
• properties <string[]> Alternate properties for constructing the table.

Try to construct a table with the columns of the properties of tabularData (or use properties) and rows of tabularData and log it. Falls back to just logging the argument if it can't be parsed as tabular.

// These can't be parsed as tabular data
console.table(Symbol());
// Symbol()

console.table(undefined);
// undefined

console.table([{ a: 1, b: 'Y' }, { a: 'Z', b: 2 }]);
// ┌─────────┬─────┬─────┐
// │ (index) │ a   │ b   │
// ├─────────┼─────┼─────┤
// │ 0       │ 1   │ 'Y' │
// │ 1       │ 'Z' │ 2   │
// └─────────┴─────┴─────┘

console.table([{ a: 1, b: 'Y' }, { a: 'Z', b: 2 }], ['a']);
// ┌─────────┬─────┐
// │ (index) │ a   │
// ├─────────┼─────┤
// │ 0       │ 1   │
// │ 1       │ 'Z' │
// └─────────┴─────┘
copy

console.time([label])#

• label <string> Default: 'default'

Starts a timer that can be used to compute the duration of an operation. Timers are identified by a unique label. Use the same label when calling console.timeEnd() to stop the timer and output the elapsed time in suitable time units to stdout. For example, if the elapsed time is 3869ms, console.timeEnd() displays "3.869s".

console.timeEnd([label])#

• label <string> Default: 'default'

Stops a timer that was previously started by calling console.time() and prints the result to stdout:

console.time('bunch-of-stuff');
// Do a bunch of stuff.
console.timeEnd('bunch-of-stuff');
// Prints: bunch-of-stuff: 225.438ms
copy

console.timeLog([label][, ...data])#

• label <string> Default: 'default'
• ...data <any>

For a timer that was previously started by calling console.time(), prints the elapsed time and other data arguments to stdout:

console.time('process');
const value = expensiveProcess1(); // Returns 42
console.timeLog('process', value);
// Prints "process: 365.227ms 42".
doExpensiveProcess2(value);
console.timeEnd('process');
copy

console.trace([message][, ...args])#

• message <any>
• ...args <any>

Prints to stderr the string 'Trace: ', followed by the util.format() formatted message and stack trace to the current position in the code.

console.trace('Show me');
// Prints: (stack trace will vary based on where trace is called)
//  Trace: Show me
//    at repl:2:9
//    at REPLServer.defaultEval (repl.js:248:27)
//    at bound (domain.js:287:14)
//    at REPLServer.runBound [as eval] (domain.js:300:12)
//    at REPLServer.<anonymous> (repl.js:412:12)
//    at emitOne (events.js:82:20)
//    at REPLServer.emit (events.js:169:7)
//    at REPLServer.Interface._onLine (readline.js:210:10)
//    at REPLServer.Interface._line (readline.js:549:8)
//    at REPLServer.Interface._ttyWrite (readline.js:826:14)
copy

console.warn([data][, ...args])#

• data <any>
• ...args <any>

The console.warn() function is an alias for console.error().

Inspector only methods#

The following methods are exposed by the V8 engine in the general API but do not display anything unless used in conjunction with the inspector (--inspect flag).

console.profile([label])#

• label <string>

This method does not display anything unless used in the inspector. The console.profile() method starts a JavaScript CPU profile with an optional label until console.profileEnd() is called. The profile is then added to the Profile panel of the inspector.

console.profile('MyLabel');
// Some code
console.profileEnd('MyLabel');
// Adds the profile 'MyLabel' to the Profiles panel of the inspector.
copy

console.profileEnd([label])#

• label <string>

This method does not display anything unless used in the inspector. Stops the current JavaScript CPU profiling session if one has been started and prints the report to the Profiles panel of the inspector. See console.profile() for an example.

If this method is called without a label, the most recently started profile is stopped.

console.timeStamp([label])#

• label <string>

This method does not display anything unless used in the inspector. The console.timeStamp() method adds an event with the label 'label' to the Timeline panel of the inspector.

Corepack#

Corepack will no longer be distributed starting with Node.js v25.

Users currently depending on the bundled corepack executable from Node.js can switch to using the userland-provided corepack module.

Crypto#

The node:crypto module provides cryptographic functionality that includes a set of wrappers for OpenSSL's hash, HMAC, cipher, decipher, sign, and verify functions.

const { createHmac } = await import('node:crypto');

const secret = 'abcdefg';
const hash = createHmac('sha256', secret)
               .update('I love cupcakes')
               .digest('hex');
console.log(hash);
// Prints:
//   c0fa1bc00531bd78ef38c628449c5102aeabd49b5dc3a2a516ea6ea959d6658e
const { createHmac } = require('node:crypto');

const secret = 'abcdefg';
const hash = createHmac('sha256', secret)
               .update('I love cupcakes')
               .digest('hex');
console.log(hash);
// Prints:
//   c0fa1bc00531bd78ef38c628449c5102aeabd49b5dc3a2a516ea6ea959d6658e
copy

Determining if crypto support is unavailable#

It is possible for Node.js to be built without including support for the node:crypto module. In such cases, attempting to import from crypto or calling require('node:crypto') will result in an error being thrown.

When using CommonJS, the error thrown can be caught using try/catch:

let crypto;
try {
  crypto = require('node:crypto');
} catch (err) {
  console.error('crypto support is disabled!');
}
copy

When using the lexical ESM import keyword, the error can only be caught if a handler for process.on('uncaughtException') is registered before any attempt to load the module is made (using, for instance, a preload module).

When using ESM, if there is a chance that the code may be run on a build of Node.js where crypto support is not enabled, consider using the import() function instead of the lexical import keyword:

let crypto;
try {
  crypto = await import('node:crypto');
} catch (err) {
  console.error('crypto support is disabled!');
}
copy

Asymmetric key types#

The following table lists the asymmetric key types recognized by the KeyObject API:

Class: Certificate#

SPKAC is a Certificate Signing Request mechanism originally implemented by Netscape and was specified formally as part of HTML5's keygen element.

<keygen> is deprecated since HTML 5.2 and new projects should not use this element anymore.

The node:crypto module provides the Certificate class for working with SPKAC data. The most common usage is handling output generated by the HTML5 <keygen> element. Node.js uses OpenSSL's SPKAC implementation internally.

Static method: Certificate.exportChallenge(spkac[, encoding])#

• spkac <string> | <ArrayBuffer> | <Buffer> | <TypedArray> | <DataView>
• encoding <string> The encoding of the spkac string.
• Returns: <Buffer> The challenge component of the spkac data structure, which includes a public key and a challenge.

const { Certificate } = await import('node:crypto');
const spkac = getSpkacSomehow();
const challenge = Certificate.exportChallenge(spkac);
console.log(challenge.toString('utf8'));
// Prints: the challenge as a UTF8 string
const { Certificate } = require('node:crypto');
const spkac = getSpkacSomehow();
const challenge = Certificate.exportChallenge(spkac);
console.log(challenge.toString('utf8'));
// Prints: the challenge as a UTF8 string
copy

Static method: Certificate.exportPublicKey(spkac[, encoding])#

• spkac <string> | <ArrayBuffer> | <Buffer> | <TypedArray> | <DataView>
• encoding <string> The encoding of the spkac string.
• Returns: <Buffer> The public key component of the spkac data structure, which includes a public key and a challenge.

const { Certificate } = await import('node:crypto');
const spkac = getSpkacSomehow();
const publicKey = Certificate.exportPublicKey(spkac);
console.log(publicKey);
// Prints: the public key as <Buffer ...>
const { Certificate } = require('node:crypto');
const spkac = getSpkacSomehow();
const publicKey = Certificate.exportPublicKey(spkac);
console.log(publicKey);
// Prints: the public key as <Buffer ...>
copy

Static method: Certificate.verifySpkac(spkac[, encoding])#

• spkac <string> | <ArrayBuffer> | <Buffer> | <TypedArray> | <DataView>
• encoding <string> The encoding of the spkac string.
• Returns: <boolean> true if the given spkac data structure is valid, false otherwise.

import { Buffer } from 'node:buffer';
const { Certificate } = await import('node:crypto');

const spkac = getSpkacSomehow();
console.log(Certificate.verifySpkac(Buffer.from(spkac)));
// Prints: true or false
const { Buffer } = require('node:buffer');
const { Certificate } = require('node:crypto');

const spkac = getSpkacSomehow();
console.log(Certificate.verifySpkac(Buffer.from(spkac)));
// Prints: true or false
copy

Legacy API#

As a legacy interface, it is possible to create new instances of the crypto.Certificate class as illustrated in the examples below.

new crypto.Certificate()#

Instances of the Certificate class can be created using the new keyword or by calling crypto.Certificate() as a function:

const { Certificate } = await import('node:crypto');

const cert1 = new Certificate();
const cert2 = Certificate();
const { Certificate } = require('node:crypto');

const cert1 = new Certificate();
const cert2 = Certificate();
copy