Node.js v23.0.0-nightly20240925773e7c67cf documentation
- Node.js v23.0.0-nightly20240925773e7c67cf
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Single executable applications#
Source Code: src/node_sea.cc
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 currently only supports running a single embedded script using the CommonJS 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.
Here are the steps for creating a single executable application using one such tool, postject:
-
Create a JavaScript file:
echo 'console.log(`Hello, ${process.argv[2]}!`);' > hello.js
-
Create a configuration file building a blob that can be injected into the single executable application (see Generating single executable preparation blobs for details):
echo '{ "main": "hello.js", "output": "sea-prep.blob" }' > sea-config.json
-
Generate the blob to be injected:
node --experimental-sea-config sea-config.json
-
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. -
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
-
Inject the blob into the copied binary by running
postject
with the following options:hello
/hello.exe
- The name of the copy of thenode
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
-
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
-
Run the binary:
- On systems other than Windows
$ ./hello world Hello, world!
- On Windows
$ .\hello.exe world Hello, world!
Generating single executable preparation blobs#
Single executable preparation blobs that are injected into the application can
be generated using the --experimental-sea-config
flag of the Node.js binary
that will be used to build the single executable. 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",
"output": "/path/to/write/the/generated/blob.blob",
"disableExperimentalSEAWarning": true, // Default: false
"useSnapshot": false, // Default: false
"useCodeCache": true, // Default: false
"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/blob.blob",
"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 } = require('node:sea');
// 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()
and sea.getRawAsset()
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 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:
- 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. - 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
.
In the injected main script#
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()
#
- Returns: <boolean> Whether this script is running inside a single-executable application.
sea.getAsset(key[, encoding])
#
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 theassets
field in the single-executable application configuration.encoding
<string> If specified, the asset will be decoded as a string. Any encoding supported by theTextDecoder
is accepted. If unspecified, anArrayBuffer
containing a copy of the asset would be returned instead.- Returns: <string> | <ArrayBuffer>
sea.getAssetAsBlob(key[, options])
#
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 theassets
field in the single-executable application configuration.options
<Object>type
<string> An optional mime type for the blob.
- Returns: <Blob>
sea.getRawAsset(key)
#
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 theassets
field in the single-executable application configuration.- Returns: <string> | <ArrayBuffer>
require(id)
in the injected main script is not file based#
require()
in the injected main script 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:
const { createRequire } = require('node:module');
require = createRequire(__filename);
__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
.
Notes#
Single executable application creation process#
A tool aiming to create a single executable Node.js application must
inject the contents of the blob prepared with --experimental-sea-config"
into:
- a resource named
NODE_SEA_BLOB
if thenode
binary is a PE file - a section named
NODE_SEA_BLOB
in theNODE_SEA
segment if thenode
binary is a Mach-O file - a note named
NODE_SEA_BLOB
if thenode
binary is an ELF file
Search 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.
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.