# Single executable applications

<!--introduced_in=REPLACEME-->

> Stability: 1 - Experimental: This feature is being designed and will change.

<!-- source_link=lib/internal/main/single_executable_application.js -->

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 JavaScript file into the `node` binary. During start up, the
program checks if anything has been injected. If the script is found, it
executes its contents. Otherwise Node.js operates as it normally does.

The single executable application feature only supports running a single
embedded [CommonJS][] file.

A bundled JavaScript file can be turned into a single executable application
with any tool which can inject resources into the `node` binary.

Here are the steps for creating a single executable application using one such
tool, [postject][]:

1. Create a JavaScript file:
   ```console
   $ echo 'console.log(`Hello, ${process.argv[2]}!`);' > hello.js
   ```

2. Create a copy of the `node` executable and name it according to your needs:
   ```console
   $ cp $(command -v node) hello
   ```

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

   * `hello` - The name of the copy of the `node` executable created in step 2.
   * `NODE_JS_CODE` - The name of the resource / note / section in the binary
     where the contents of the JavaScript file will be stored.
   * `hello.js` - The name of the JavaScript file created in step 1.
   * `--sentinel-fuse NODE_JS_FUSE_fce680ab2cc467b6e072b8b5df1996b2` - The
     [fuse][] used by the Node.js project to detect if a file has been injected.
   * `--macho-segment-name NODE_JS` (only needed on macOS) - The name of the
     segment in the binary where the contents of the JavaScript file will be
     stored.

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

   * On systems other than macOS:
     ```console
     $ npx postject hello NODE_JS_CODE hello.js \
         --sentinel-fuse NODE_JS_FUSE_fce680ab2cc467b6e072b8b5df1996b2
     ```

   * On macOS:
     ```console
     $ npx postject hello NODE_JS_CODE hello.js \
         --sentinel-fuse NODE_JS_FUSE_fce680ab2cc467b6e072b8b5df1996b2 \
         --macho-segment-name NODE_JS
     ```

4. Run the binary:
   ```console
   $ ./hello world
   Hello, world!
   ```

## Notes

### `require(id)` in the injected module is not file based

`require()` in the injected module is not the same as the [`require()`][]
available to modules that are not injected. It also does not have any of the
properties that non-injected [`require()`][] has except [`require.main`][]. It
can only be used to load built-in modules. Attempting to load a module that can
only be found in the file system will throw an error.

Instead of relying on a file based `require()`, users can bundle their
application into a standalone JavaScript file to inject into the executable.
This also ensures a more deterministic dependency graph.

However, if a file based `require()` is still needed, that can also be achieved:

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

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

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

### `__dirname` in the injected module

The value of `__dirname` in the injected module is equal to the directory name
of [`process.execPath`][].

### Single executable application creation process

A tool aiming to create a single executable Node.js application must
inject the contents of a JavaScript file into:

* a resource named `NODE_JS_CODE` if the `node` binary is a [PE][] file
* a section named `NODE_JS_CODE` in the `NODE_JS` segment if the `node` binary
  is a [Mach-O][] file
* a note named `NODE_JS_CODE` if the `node` binary is an [ELF][] file

Search the binary for the
`NODE_JS_FUSE_fce680ab2cc467b6e072b8b5df1996b2:0` [fuse][] string and flip the
last character to `1` to indicate that a resource has been injected.

### Platform support

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

* Windows
* macOS
* Linux (AMD64 only)

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.

[CommonJS]: modules.md#modules-commonjs-modules
[ELF]: https://en.wikipedia.org/wiki/Executable_and_Linkable_Format
[Mach-O]: https://en.wikipedia.org/wiki/Mach-O
[PE]: https://en.wikipedia.org/wiki/Portable_Executable
[`process.execPath`]: process.md#processexecpath
[`require()`]: modules.md#requireid
[`require.main`]: modules.md#accessing-the-main-module
[fuse]: https://www.electronjs.org/docs/latest/tutorial/fuses
[postject]: https://github.com/nodejs/postject
[single executable applications]: https://github.com/nodejs/single-executable
