electron/docs/development/source-code-directory-structure.md

# Source Code Directory Structure

The source code of Electron is separated into a few parts, mostly
following Chromium on the separation conventions.

You may need to become familiar with [Chromium's multi-process
architecture](https://dev.chromium.org/developers/design-documents/multi-process-architecture)
to understand the source code better.

## Structure of Source Code

```diff
Electron
├── atom/ - C++ source code.
|   ├── app/ - System entry code.
|   ├── browser/ - The frontend including the main window, UI, and all of the
|   |   |          main process things. This talks to the renderer to manage web
|   |   |          pages.
|   |   ├── ui/ - Implementation of UI stuff for different platforms.
|   |   |   ├── cocoa/ - Cocoa specific source code.
|   |   |   ├── win/ - Windows GUI specific source code.
|   |   |   └── x/ - X11 specific source code.
|   |   ├── api/ - The implementation of the main process APIs.
|   |   ├── net/ - Network related code.
|   |   ├── mac/ - Mac specific Objective-C source code.
|   |   └── resources/ - Icons, platform-dependent files, etc.
|   ├── renderer/ - Code that runs in renderer process.
|   |   └── api/ - The implementation of renderer process APIs.
|   └── common/ - Code that used by both the main and renderer processes,
|       |         including some utility functions and code to integrate node's
|       |         message loop into Chromium's message loop.
|       └── api/ - The implementation of common APIs, and foundations of
|                  Electron's built-in modules.
├── chromium_src/ - Source code copied from Chromium. See below.
├── default_app/ - The default page to show when Electron is started without
|                  providing an app.
├── docs/ - Documentations.
├── lib/ - JavaScript source code.
|   ├── browser/ - Javascript main process initialization code.
|   |   └── api/ - Javascript API implementation.
|   ├── common/ - JavaScript used by both the main and renderer processes
|   |   └── api/ - Javascript API implementation.
|   └── renderer/ - Javascript renderer process initialization code.
|       └── api/ - Javascript API implementation.
├── native_mate/ - A fork of Chromium's gin library that makes it easier to marshal
|                  types between C++ and JavaScript.
├── spec/ - Automatic tests.
└── BUILD.gn - Building rules of Electron.
```

## `/chromium_src`

The files in `/chromium_src` tend to be pieces of Chromium that aren't part of
the content layer. For example to implement Pepper API, we need some wiring
similar to what official Chrome does. We could have built the relevant
sources as a part of [libcc](../glossary.md#libchromiumcontent) but most
often we don't require all the features (some tend to be proprietary,
analytics stuff) so we took parts of the code. These could have easily
been patches in libcc, but at the time when these were written the goal of
libcc was to maintain very minimal patches and chromium_src changes tend to be
big ones. Also, note that these patches can never be upstreamed unlike other
libcc patches we maintain now.

## Structure of Other Directories

* **script** - Scripts used for development purpose like building, packaging,
  testing, etc.
* **tools** - Helper scripts used by GN files, unlike `script`, scripts put
  here should never be invoked by users directly.
* **vendor** - Source code of third party dependencies, we didn't use
  `third_party` as name because it would confuse it with the same directory in
  Chromium's source code tree.
* **node_modules** - Third party node modules used for building.
* **out** - Temporary output directory of `ninja`.
* **dist** - Temporary directory created by `script/create-dist.py` script
  when creating a distribution.
* **external_binaries** - Downloaded binaries of third-party frameworks which
  do not support building with `gn`.

## Keeping Git Submodules Up to Date

The Electron repository has a few vendored dependencies, found in the
[/vendor][vendor] directory. Occasionally you might see a message like this
when running `git status`:

```sh
$ git status

	modified:   vendor/depot_tools (new commits)
	modified:   vendor/boto (new commits)
```

To update these vendored dependencies, run the following command:

```sh
git submodule update --init --recursive
```

If you find yourself running this command often, you can create an alias for it
in your `~/.gitconfig` file:

```sh
[alias]
	su = submodule update --init --recursive
```

[vendor]: https://github.com/electron/electron/tree/master/vendor