Single executable applications | Node.js v26.0.0 Documentation

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Table of contents

- Single executable applications
  - Generating single executable applications with `--build-sea`
    - Assets
    - Startup snapshot support
    - V8 code cache support
    - Execution arguments
    - Execution argument extension
  - Single-executable application API
    - `sea.isSea()`
    - `sea.getAsset(key[, encoding])`
    - `sea.getAssetAsBlob(key[, options])`
    - `sea.getRawAsset(key)`
    - `sea.getAssetKeys()`
  - In the injected main script
    - Module format of the injected main script
    - Module loading in the injected main script
    - `require()` in the injected main script
    - `__filename` and `module.filename` in the injected main script
    - `__dirname` in the injected main script
    - `import.meta` in the injected main script
    - `import()` in the injected main script
    - Using native addons in the injected main script
  - Notes
    - Single executable application creation process
      - 1. Generating single executable preparation blobs
        - Dumping the preparation blob to disk
      - 2. Injecting the preparation blob into the `node` binary
        - Injecting the preparation blob manually
    - Platform support

## Single executable applications#

Source Code: src/node_sea.cc Added in: v19.7.0, v18.16.0
History

Version | Changes
--- | ---
v25.5.0 | Added built-in single executable application generation via the CLI flag `--build-sea`.
v20.6.0 | Added support for "useSnapshot".
v20.6.0 | Added support for "useCodeCache".

Stability: 1.1 - Active development

This feature allows the distribution of a Node.js application conveniently to a system that does not have Node.js installed.

Node.js supports the creation of single executable applications by allowing the injection of a blob prepared by Node.js, which can contain a bundled script, into the `node` binary. During start up, the program checks if anything has been injected. If the blob is found, it executes the script in the blob. Otherwise Node.js operates as it normally does.

The single executable application feature supports running a single embedded script using the CommonJS or the ECMAScript Modules module system.

Users can create a single executable application from their bundled script with the `node` binary itself and any tool which can inject resources into the binary.

1. Create a JavaScript file:

       echo 'console.log(`Hello, ${process.argv[2]}!`);' > hello.js

2. Create a configuration file building a blob that can be injected into the single executable application (see Generating single executable preparation blobs for details):

   - On systems other than Windows:

       echo '{ "main": "hello.js", "output": "sea" }' > sea-config.json

   - On Windows:

       echo '{ "main": "hello.js", "output": "sea.exe" }' > sea-config.json

   The `.exe` extension is necessary.

3. Generate the target executable:

       node --build-sea sea-config.json

4. Sign the binary (macOS and Windows only):

   - On macOS:

       codesign --sign - hello

   - On Windows (optional):

   A certificate needs to be present for this to work. However, the unsigned binary would still be runnable.

       signtool sign /fd SHA256 hello.exe

5. Run the binary:

   - On systems other than Windows

       $ ./hello world
       Hello, world!

   - On Windows

       $ .\hello.exe world
       Hello, world!

### Generating single executable applications with `--build-sea`#

To generate a single executable application directly, the `--build-sea` flag can be used. It takes a path to a configuration file in JSON format. If the path passed to it isn't absolute, Node.js will use the path relative to the current working directory.

The configuration currently reads the following top-level fields:

    {
      "main": "/path/to/bundled/script.js",
      "mainFormat": "commonjs", // Default: "commonjs", options: "commonjs", "module"
      "executable": "/path/to/node/binary", // Optional, if not specified, uses the current Node.js binary
      "output": "/path/to/write/the/generated/executable",
      "disableExperimentalSEAWarning": true, // Default: false
      "useSnapshot": false,  // Default: false
      "useCodeCache": true, // Default: false
      "execArgv": ["--no-warnings", "--max-old-space-size=4096"], // Optional
      "execArgvExtension": "env", // Default: "env", options: "none", "env", "cli"
      "assets": {  // Optional
        "a.dat": "/path/to/a.dat",
        "b.txt": "/path/to/b.txt"
      }
    }

If the paths are not absolute, Node.js will use the path relative to the current working directory. The version of the Node.js binary used to produce the blob must be the same as the one to which the blob will be injected.

Note: When generating cross-platform SEAs (e.g., generating a SEA for `linux-x64` on `darwin-arm64`), `useCodeCache` and `useSnapshot` must be set to false to avoid generating incompatible executables. Since code cache and snapshots can only be loaded on the same platform where they are compiled, the generated executable might crash on startup when trying to load code cache or snapshots built on a different platform.

#### Assets#

Users can include assets by adding a key-path dictionary to the configuration as the `assets` field. At build time, Node.js would read the assets from the specified paths and bundle them into the preparation blob. In the generated executable, users can retrieve the assets using the `sea.getAsset()` and `sea.getAssetAsBlob()` APIs.

    {
      "main": "/path/to/bundled/script.js",
      "output": "/path/to/write/the/generated/executable",
      "assets": {
        "a.jpg": "/path/to/a.jpg",
        "b.txt": "/path/to/b.txt"
      }
    }

The single-executable application can access the assets as follows:

    const { getAsset, getAssetAsBlob, getRawAsset, getAssetKeys } = require('node:sea');
    // Get all asset keys.
    const keys = getAssetKeys();
    console.log(keys); // ['a.jpg', 'b.txt']
    // Returns a copy of the data in an ArrayBuffer.
    const image = getAsset('a.jpg');
    // Returns a string decoded from the asset as UTF8.
    const text = getAsset('b.txt', 'utf8');
    // Returns a Blob containing the asset.
    const blob = getAssetAsBlob('a.jpg');
    // Returns an ArrayBuffer containing the raw asset without copying.
    const raw = getRawAsset('a.jpg');

See documentation of the `sea.getAsset()`, `sea.getAssetAsBlob()`, `sea.getRawAsset()` and `sea.getAssetKeys()` APIs for more information.

#### Startup snapshot support#

The `useSnapshot` field can be used to enable startup snapshot support. In this case, the `main` script would not be executed when the final executable is launched. Instead, it would be run when the single executable application preparation blob is generated on the building machine. The generated preparation blob would then include a snapshot capturing the states initialized by the `main` script. The final executable, with the preparation blob injected, would deserialize the snapshot at run time.

When `useSnapshot` is true, the main script must invoke the `v8.startupSnapshot.setDeserializeMainFunction()` API to configure code that needs to be run when the final executable is launched by the users.

The typical pattern for an application to use snapshot in a single executable application is:

1. At build time, on the building machine, the main script is run to initialize the heap to a state that's ready to take user input. The script should also configure a main function with `v8.startupSnapshot.setDeserializeMainFunction()`. This function will be compiled and serialized into the snapshot, but not invoked at build time.
2. At run time, the main function will be run on top of the deserialized heap on the user machine to process user input and generate output.

The general constraints of the startup snapshot scripts also apply to the main script when it's used to build snapshot for the single executable application, and the main script can use the `v8.startupSnapshot` API to adapt to these constraints. See documentation about startup snapshot support in Node.js.

#### V8 code cache support#

When `useCodeCache` is set to `true` in the configuration, during the generation of the single executable preparation blob, Node.js will compile the `main` script to generate the V8 code cache. The generated code cache would be part of the preparation blob and get injected into the final executable. When the single executable application is launched, instead of compiling the `main` script from scratch, Node.js would use the code cache to speed up the compilation, then execute the script, which would improve the startup performance.

Note: `import()` does not work when `useCodeCache` is `true`.

#### Execution arguments#

The `execArgv` field can be used to specify Node.js-specific arguments that will be automatically applied when the single executable application starts. This allows application developers to configure Node.js runtime options without requiring end users to be aware of these flags.

For example, the following configuration:

    {
      "main": "/path/to/bundled/script.js",
      "output": "/path/to/write/the/generated/executable",
      "execArgv": ["--no-warnings", "--max-old-space-size=2048"]
    }

will instruct the SEA to be launched with the `--no-warnings` and `--max-old-space-size=2048` flags. In the scripts embedded in the executable, these flags can be accessed using the `process.execArgv` property:

    // If the executable is launched with `sea user-arg1 user-arg2`
    console.log(process.execArgv);
    // Prints: ['--no-warnings', '--max-old-space-size=2048']
    console.log(process.argv);
    // Prints ['/path/to/sea', 'path/to/sea', 'user-arg1', 'user-arg2']

The user-provided arguments are in the `process.argv` array starting from index 2, similar to what would happen if the application is started with:

    node --no-warnings --max-old-space-size=2048 /path/to/bundled/script.js user-arg1 user-arg2

#### Execution argument extension#

The `execArgvExtension` field controls how additional execution arguments can be provided beyond those specified in the `execArgv` field. It accepts one of three string values:

- `"none"`: No extension is allowed. Only the arguments specified in `execArgv` will be used, and the `NODE_OPTIONS` environment variable will be ignored.
- `"env"`: (Default) The `NODE_OPTIONS` environment variable can extend the execution arguments. This is the default behavior to maintain backward compatibility.
- `"cli"`: The executable can be launched with `--node-options="--flag1 --flag2"`, and those flags will be parsed as execution arguments for Node.js instead of being passed to the user script. This allows using arguments that are not supported by the `NODE_OPTIONS` environment variable.

For example, with `"execArgvExtension": "cli"`:

    {
      "main": "/path/to/bundled/script.js",
      "output": "/path/to/write/the/generated/executable",
      "execArgv": ["--no-warnings"],
      "execArgvExtension": "cli"
    }

The executable can be launched as:

    ./my-sea --node-options="--trace-exit" user-arg1 user-arg2

This would be equivalent to running:

    node --no-warnings --trace-exit /path/to/bundled/script.js user-arg1 user-arg2

### Single-executable application API#

The `node:sea` builtin allows interaction with the single-executable application from the JavaScript main script embedded into the executable.

#### `sea.isSea()`#

Added in: v21.7.0, v20.12.0

- Returns: `<boolean>` Whether this script is running inside a single-executable application.

#### `sea.getAsset(key[, encoding])`#

Added in: v21.7.0, v20.12.0

This method can be used to retrieve the assets configured to be bundled into the single-executable application at build time. An error is thrown when no matching asset can be found.

- `key` `<string>` the key for the asset in the dictionary specified by the `assets` field in the single-executable application configuration.
- `encoding` `<string>` If specified, the asset will be decoded as a string. Any encoding supported by the `TextDecoder` is accepted. If unspecified, an `ArrayBuffer` containing a copy of the asset would be returned instead.
- Returns: `<string>` | `<ArrayBuffer>`

#### `sea.getAssetAsBlob(key[, options])`#

Added in: v21.7.0, v20.12.0

Similar to `sea.getAsset()`, but returns the result in a `<Blob>`. An error is thrown when no matching asset can be found.

- `key` `<string>` the key for the asset in the dictionary specified by the `assets` field in the single-executable application configuration.
- `options` `<Object>`
  - `type` `<string>` An optional mime type for the blob.
- Returns: `<Blob>`

#### `sea.getRawAsset(key)`#

Added in: v21.7.0, v20.12.0

This method can be used to retrieve the assets configured to be bundled into the single-executable application at build time. An error is thrown when no matching asset can be found.

Unlike `sea.getAsset()` or `sea.getAssetAsBlob()`, this method does not return a copy. Instead, it returns the raw asset bundled inside the executable.

For now, users should avoid writing to the returned array buffer. If the injected section is not marked as writable or not aligned properly, writes to the returned array buffer is likely to result in a crash.

- `key` `<string>` the key for the asset in the dictionary specified by the `assets` field in the single-executable application configuration.
- Returns: `<ArrayBuffer>`

#### `sea.getAssetKeys()`#

Added in: v24.8.0, v22.20.0

- Returns `<string[]>` An array containing all the keys of the assets embedded in the executable. If no assets are embedded, returns an empty array.

This method can be used to retrieve an array of all the keys of assets embedded into the single-executable application. An error is thrown when not running inside a single-executable application.

### In the injected main script#

#### Module format of the injected main script#

To specify how Node.js should interpret the injected main script, use the `mainFormat` field in the single-executable application configuration. The accepted values are:

- `"commonjs"`: The injected main script is treated as a CommonJS module.
- `"module"`: The injected main script is treated as an ECMAScript module.

If the `mainFormat` field is not specified, it defaults to `"commonjs"`.

Currently, `"mainFormat": "module"` cannot be used together with `"useSnapshot"`.

#### Module loading in the injected main script#

In the injected main script, module loading does not read from the file system. By default, both `require()` and `import` statements would only be able to load the built-in modules. Attempting to load a module that can only be found in the file system will throw an error.

Users can bundle their application into a standalone JavaScript file to inject into the executable. This also ensures a more deterministic dependency graph.

To load modules from the file system in the injected main script, users can create a `require` function that can load from the file system using `module.createRequire()`. For example, in a CommonJS entry point:

    const { createRequire } = require('node:module');
    require = createRequire(__filename);

#### `require()` in the injected main script#

`require()` in the injected main script is not the same as the `require()` available to modules that are not injected. Currently, it does not have any of the properties that non-injected `require()` has except `require.main`.

#### `__filename` and `module.filename` in the injected main script#

The values of `__filename` and `module.filename` in the injected main script are equal to `process.execPath`.

#### `__dirname` in the injected main script#

The value of `__dirname` in the injected main script is equal to the directory name of `process.execPath`.

#### `import.meta` in the injected main script#

When using `"mainFormat": "module"`, `import.meta` is available in the injected main script with the following properties:

- `import.meta.url`: A `file:` URL corresponding to `process.execPath`.
- `import.meta.filename`: Equal to `process.execPath`.
- `import.meta.dirname`: The directory name of `process.execPath`.
- `import.meta.main`: `true`.

`import.meta.resolve` is currently not supported.

#### `import()` in the injected main script#

When using `"mainFormat": "module"`, `import()` can be used to dynamically load built-in modules. Attempting to use `import()` to load modules from the file system will throw an error.

#### Using native addons in the injected main script#

Native addons can be bundled as assets into the single-executable application by specifying them in the `assets` field of the configuration file used to generate the single-executable application preparation blob. The addon can then be loaded in the injected main script by writing the asset to a temporary file and loading it with `process.dlopen()`.

    {
      "main": "/path/to/bundled/script.js",
      "output": "/path/to/write/the/generated/executable",
      "assets": {
        "myaddon.node": "/path/to/myaddon/build/Release/myaddon.node"
      }
    }

    // script.js
    const fs = require('node:fs');
    const os = require('node:os');
    const path = require('node:path');
    const { getRawAsset } = require('node:sea');
    const addonPath = path.join(os.tmpdir(), 'myaddon.node');
    fs.writeFileSync(addonPath, new Uint8Array(getRawAsset('myaddon.node')));
    const myaddon = { exports: {} };
    process.dlopen(myaddon, addonPath);
    console.log(myaddon.exports);
    fs.rmSync(addonPath);

Known caveat: if the single-executable application is produced by postject running on a Linux arm64 docker container, the produced ELF binary does not have the correct hash table to load the addons and will crash on `process.dlopen()`. Build the single-executable application on other platforms, or at least on a non-container Linux arm64 environment to work around this issue.

### Notes#

#### Single executable application creation process#

The process documented here is subject to change.

##### 1. Generating single executable preparation blobs#

To build a single executable application, Node.js would first generate a blob that contains all the necessary information to run the bundled script. When using `--build-sea`, this step is done internally along with the injection.

###### Dumping the preparation blob to disk#

Before `--build-sea` was introduced, an older workflow was introduced to write the preparation blob to disk for injection by external tools. This can still be used for verification purposes.

To dump the preparation blob to disk for verification, use `--experimental-sea-config`. This writes a file that can be injected into a Node.js binary using tools like postject.

The configuration is similar to that of `--build-sea`, except that the `output` field specifies the path to write the generated blob file instead of the final executable.

    {
      "main": "/path/to/bundled/script.js",
      // Instead of the final executable, this is the path to write the blob.
      "output": "/path/to/write/the/generated/blob.blob"
    }

##### 2. Injecting the preparation blob into the `node` binary#

To complete the creation of a single executable application, the generated blob needs to be injected into a copy of the `node` binary, as documented below.

When using `--build-sea`, this step is done internally along with the blob generation.

- If the `node` binary is a PE file, the blob should be injected as a resource named `NODE_SEA_BLOB`.
- If the `node` binary is a Mach-O file, the blob should be injected as a section named `NODE_SEA_BLOB` in the `NODE_SEA` segment.
- If the `node` binary is an ELF file, the blob should be injected as a note named `NODE_SEA_BLOB`.

Then, the SEA building process searches the binary for the `NODE_SEA_FUSE_fce680ab2cc467b6e072b8b5df1996b2:0` fuse string and flip the last character to `1` to indicate that a resource has been injected.

###### Injecting the preparation blob manually#

Before `--build-sea` was introduced, an older workflow was introduced to allow external tools to inject the generated blob into a copy of the `node` binary.

For example, with postject:

1. Create a copy of the `node` executable and name it according to your needs:

   - On systems other than Windows:

       cp $(command -v node) hello

   - On Windows:

       node -e "require('fs').copyFileSync(process.execPath, 'hello.exe')"

   The `.exe` extension is necessary.

2. Remove the signature of the binary (macOS and Windows only):

   - On macOS:

       codesign --remove-signature hello

   - On Windows (optional):

   signtool can be used from the installed Windows SDK. If this step is skipped, ignore any signature-related warning from postject.

       signtool remove /s hello.exe

3. Inject the blob into the copied binary by running `postject` with the following options:

   - `hello` / `hello.exe` - The name of the copy of the `node` executable created in step 4.
   - `NODE_SEA_BLOB` - The name of the resource / note / section in the binary where the contents of the blob will be stored.
   - `sea-prep.blob` - The name of the blob created in step 1.
   - `--sentinel-fuse NODE_SEA_FUSE_fce680ab2cc467b6e072b8b5df1996b2` - The fuse used by the Node.js project to detect if a file has been injected.
   - `--macho-segment-name NODE_SEA` (only needed on macOS) - The name of the segment in the binary where the contents of the blob will be stored.

   To summarize, here is the required command for each platform:

   - On Linux:

         npx postject hello NODE_SEA_BLOB sea-prep.blob \
             --sentinel-fuse NODE_SEA_FUSE_fce680ab2cc467b6e072b8b5df1996b2

   - On Windows - PowerShell:

         npx postject hello.exe NODE_SEA_BLOB sea-prep.blob `
             --sentinel-fuse NODE_SEA_FUSE_fce680ab2cc467b6e072b8b5df1996b2

   - On Windows - Command Prompt:

         npx postject hello.exe NODE_SEA_BLOB sea-prep.blob ^
             --sentinel-fuse NODE_SEA_FUSE_fce680ab2cc467b6e072b8b5df1996b2

   - On macOS:

         npx postject hello NODE_SEA_BLOB sea-prep.blob \
             --sentinel-fuse NODE_SEA_FUSE_fce680ab2cc467b6e072b8b5df1996b2 \
             --macho-segment-name NODE_SEA

#### Platform support#

Single-executable support is tested regularly on CI only on the following platforms:

- Windows
- macOS
- Linux (all distributions supported by Node.js except Alpine and all architectures supported by Node.js except s390x)

This is due to a lack of better tools to generate single-executables that can be used to test this feature on other platforms.

Suggestions for other resource injection tools/workflows are welcomed. Please start a discussion at https://github.com/nodejs/single-executable/discussions to help us document them.