electron/docs/tutorial/quick-start.md

Quick start

Introduction

Electron enables you to create desktop applications with pure JavaScript by providing a runtime with rich native APIs. You could see it as a variant of the io.js runtime which is focused on desktop applications instead of web servers.

This doesn't mean Electron is a JavaScript binding to GUI libraries. Instead, Electron uses web pages as its GUI, so you could also see it as a minimal Chromium browser, controlled by JavaScript.

Main process

In Electron, the process that runs package.json's main script is called the main process. The script that runs in the main process can display a GUI by creating web pages.

Renderer process

Since Electron uses Chromium for displaying web pages, Chromium's multi-process architecture is also used. Each web page in Electron runs in its own process, which is called the renderer process.

In normal browsers, web pages usually run in a sandboxed environment and are not allowed access to native resources. Electron users, however, have the power to use io.js APIs in web pages allowing lower level operating system interactions.

Differences between main process and renderer process

The main process creates web pages by creating BrowserWindow instances. Each BrowserWindow instance runs the web page in its own renderer process. When a BrowserWindow instance is destroyed, the corresponding renderer process is also terminated.

The main process manages all web pages and their corresponding renderer processes. Each renderer process is isolated and only cares about the web page running in it.

In web pages, it is not allowed to call native GUI related APIs because managing native GUI resources in web pages is very dangerous and it is easy to leak resources. If you want to perform GUI operations in a web page, the renderer process of the web page must communicate with the main process to request the main process perform those operations.

In Electron, we have provided the ipc module for communication between main process and renderer process. And there is also a remote module for RPC style communication.

Write your first Electron app

Generally, an Electron app would be structured like this:

your-app/
├── package.json
├── main.js
└── index.html

The format of package.json is exactly the same as that of Node's modules, and the script specified by the main field is the startup script of your app, which will run on the main process. An example of your package.json might look like this:

{
  "name"    : "your-app",
  "version" : "0.1.0",
  "main"    : "main.js"
}

The main.js should create windows and handle system events, a typical example being:

var app = require('app');  // Module to control application life.
var BrowserWindow = require('browser-window');  // Module to create native browser window.

// Report crashes to our server.
require('crash-reporter').start();

// Keep a global reference of the window object, if you don't, the window will
// be closed automatically when the JavaScript object is GCed.
var mainWindow = null;

// Quit when all windows are closed.
app.on('window-all-closed', function() {
  // On OS X it is common for applications and their menu bar
  // to stay active until the user quits explicitly with Cmd + Q
  if (process.platform != 'darwin') {
    app.quit();
  }
});

// This method will be called when Electron has finished
// initialization and is ready to create browser windows.
app.on('ready', function() {
  // Create the browser window.
  mainWindow = new BrowserWindow({width: 800, height: 600});

  // and load the index.html of the app.
  mainWindow.loadUrl('file://' + __dirname + '/index.html');

  // Open the devtools.
  mainWindow.openDevTools();

  // Emitted when the window is closed.
  mainWindow.on('closed', function() {
    // Dereference the window object, usually you would store windows
    // in an array if your app supports multi windows, this is the time
    // when you should delete the corresponding element.
    mainWindow = null;
  });
});

Finally the index.html is the web page you want to show:

<!DOCTYPE html>
<html>
  <head>
    <title>Hello World!</title>
  </head>
  <body>
    <h1>Hello World!</h1>
    We are using io.js <script>document.write(process.version)</script>
    and Electron <script>document.write(process.versions['electron'])</script>.
  </body>
</html>

Run your app

After you're done writing your app, you can create a distribution by following the Application distribution guide and then execute the packaged app. You can also just use the downloaded Electron binary to execute your app directly.

On Windows:

$ .\electron\electron.exe your-app\

On Linux:

$ ./electron/electron your-app/

On OS X:

$ ./Electron.app/Contents/MacOS/Electron your-app/

Electron.app here is part of the Electron's release package, you can download it from here.