electron/docs/tutorial/using-native-node-modules.md

Using Native Node Modules

Native Node modules are supported by Electron, but since Electron is very likely to use a different V8 version from the Node binary installed on your system, the modules you use will need to be recompiled for Electron. Otherwise, you will get the following class of error when you try to run your app:

Error: The module '/path/to/native/module.node'
was compiled against a different Node.js version using
NODE_MODULE_VERSION $XYZ. This version of Node.js requires
NODE_MODULE_VERSION $ABC. Please try re-compiling or re-installing
the module (for instance, using `npm rebuild` or `npm install`).

How to install native modules

There are several different ways to install native modules:

Installing modules and rebuilding for Electron

You can install modules like other Node projects, and then rebuild the modules for Electron with the electron-rebuild package. This module can automatically determine the version of Electron and handle the manual steps of downloading headers and rebuilding native modules for your app.

For example, to install electron-rebuild and then rebuild modules with it via the command line:

npm install --save-dev electron-rebuild

# Every time you run "npm install", run this:
./node_modules/.bin/electron-rebuild

# On Windows if you have trouble, try:
.\node_modules\.bin\electron-rebuild.cmd

For more information on usage and integration with other tools, consult the project's README.

Using npm

By setting a few environment variables, you can use npm to install modules directly.

For example, to install all dependencies for Electron:

# Electron's version.
export npm_config_target=1.2.3
# The architecture of Electron, see https://electronjs.org/docs/tutorial/support#supported-platforms
# for supported architectures.
export npm_config_arch=x64
export npm_config_target_arch=x64
# Download headers for Electron.
export npm_config_disturl=https://atom.io/download/electron
# Tell node-pre-gyp that we are building for Electron.
export npm_config_runtime=electron
# Tell node-pre-gyp to build module from source code.
export npm_config_build_from_source=true
# Install all dependencies, and store cache to ~/.electron-gyp.
HOME=~/.electron-gyp npm install

Manually building for Electron

If you are a developer developing a native module and want to test it against Electron, you might want to rebuild the module for Electron manually. You can use node-gyp directly to build for Electron:

cd /path-to-module/
HOME=~/.electron-gyp node-gyp rebuild --target=1.2.3 --arch=x64 --dist-url=https://atom.io/download/electron

• HOME=~/.electron-gyp changes where to find development headers.
• --target=1.2.3 is the version of Electron.
• --dist-url=... specifies where to download the headers.
• --arch=x64 says the module is built for a 64-bit system.

Manually building for a custom build of Electron

To compile native Node modules against a custom build of Electron that doesn't match a public release, instruct npm to use the version of Node you have bundled with your custom build.

npm rebuild --nodedir=/path/to/electron/vendor/node

Troubleshooting

If you installed a native module and found it was not working, you need to check the following things:

• When in doubt, run electron-rebuild first.
• Make sure the native module is compatible with the target platform and architecture for your Electron app.
• Make sure win_delay_load_hook is not set to false in the module's binding.gyp.
• After you upgrade Electron, you usually need to rebuild the modules.

A note about win_delay_load_hook

On Windows, by default, node-gyp links native modules against node.dll. However, in Electron 4.x and higher, the symbols needed by native modules are exported by electron.exe, and there is no node.dll. In order to load native modules on Windows, node-gyp installs a delay-load hook that triggers when the native module is loaded, and redirects the node.dll reference to use the loading executable instead of looking for node.dll in the library search path (which would turn up nothing). As such, on Electron 4.x and higher, 'win_delay_load_hook': 'true' is required to load native modules.

If you get an error like Module did not self-register, or The specified procedure could not be found, it may mean that the module you're trying to use did not correctly include the delay-load hook. If the module is built with node-gyp, ensure that the win_delay_load_hook variable is set to true in the binding.gyp file, and isn't getting overridden anywhere. If the module is built with another system, you'll need to ensure that you build with a delay-load hook installed in the main .node file. Your link.exe invocation should look like this:

 link.exe /OUT:"foo.node" "...\node.lib" delayimp.lib /DELAYLOAD:node.exe /DLL
     "my_addon.obj" "win_delay_load_hook.obj"

In particular, it's important that:

• you link against node.lib from Electron and not Node. If you link against the wrong node.lib you will get load-time errors when you require the module in Electron.
• you include the flag /DELAYLOAD:node.exe. If the node.exe link is not delayed, then the delay-load hook won't get a chance to fire and the node symbols won't be correctly resolved.
• win_delay_load_hook.obj is linked directly into the final DLL. If the hook is set up in a dependent DLL, it won't fire at the right time.

See node-gyp for an example delay-load hook if you're implementing your own.

Modules that rely on prebuild

prebuild provides a way to publish native Node modules with prebuilt binaries for multiple versions of Node and Electron.

If modules provide binaries for the usage in Electron, make sure to omit --build-from-source and the npm_config_build_from_source environment variable in order to take full advantage of the prebuilt binaries.

Modules that rely on node-pre-gyp

The node-pre-gyp tool provides a way to deploy native Node modules with prebuilt binaries, and many popular modules are using it.

Usually those modules work fine under Electron, but sometimes when Electron uses a newer version of V8 than Node and/or there are ABI changes, bad things may happen. So in general, it is recommended to always build native modules from source code. electron-rebuild handles this for you automatically.

If you are following the npm way of installing modules, then this is done by default, if not, you have to pass --build-from-source to npm, or set the npm_config_build_from_source environment variable.