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

Using Native Node Modules

The native Node modules are supported by Electron, but since Electron is very likely to use a different V8 version from the Node binary installed in your system, you have to manually specify the location of Electron's headers when building native modules.

How to install native modules

Three ways to install native modules:

Using npm

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

An example of installing all dependencies for Electron:

# Electron's version.
export npm_config_target=1.2.3
# The architecture of Electron, can be ia32 or x64.
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

Installing modules and rebuilding for Electron

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

An example of installing electron-rebuild and then rebuild modules with it:

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

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

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

Manually building for a custom build of Electron

To compile native Node addons 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=$HOME/.../path/to/electron/vendor/node

Troubleshooting

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

• The architecture of the module has to match Electron's architecture (ia32 or x64).
• 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.
• When in doubt, run electron-rebuild first.

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 Electron 4.x. 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 there are ABI changes, bad things may happen. So in general it is recommended to always build native modules from source code.

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.