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Writing Your First Electron JS App

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admin
posted
May 2, 2018
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Electron enables you to create desktop applications with pure JavaScript by providing a runtime with rich native (operating system) APIs. You could see it as a variant of the Node.js runtime that is focused on desktop applications instead of web servers. This doesn’t mean Electron is a JavaScript binding to graphical user interface (GUI) libraries. Instead, Electron uses web pages as its GUI, so you could also see it as a minimal Chromium browser, controlled by JavaScript. Note: This example is also available as a repository you can download and run immediately. As far as development is concerned, an Electron application is essentially a Node.js application. The starting point is a package.json that is identical to that of a Node.js module. A most basic Electron app would have the following folder structure:
your-app/
  ├── package.json
  ├── main.js
  └── index.html
Create a new empty folder for your new Electron application. Open up your command line client and run npm init from that very folder.
npm init
npm will guide you through creating a basic package.json file. The script specified by the main field is the startup script of your app, which will run the main process. An example of your package.json might look like this:
{
    "name": "your-app",
    "version": "0.1.0",
    "main": "main.js"
  }
Note: If the main field is not present in package.json, Electron will attempt to load an index.js (just like Node.js itself). If this was actually a simple Node application, you would add a start script that instructs node to execute the current package:
{
    "name": "your-app",
    "version": "0.1.0",
    "main": "main.js",
    "scripts": {
      "start": "node ."
    }
  }
Turning this Node application into an Electron application is quite simple – we merely replace the node runtime with the electron runtime.
{
    "name": "your-app",
    "version": "0.1.0",
    "main": "main.js",
    "scripts": {
      "start": "electron ."
    }
  }

Installing Electron

At this point, you’ll need to install electron itself. The recommended way of doing so is to install it as a development dependency in your app, which allows you to work on multiple apps with different Electron versions. To do so, run the following command from your app’s directory:
npm install --save-dev electron
Other means for installing Electron exist. Please consult the installation guide to learn about use with proxies, mirrors, and custom caches.
Electron apps are developed in JavaScript using the same principles and methods found in Node.js development. All APIs and features found in Electron are accessible through the electron module, which can be required like any other Node.js module:
const electron = require('electron')
The electron module exposes features in namespaces. As examples, the lifecycle of the application is managed through electron.app, windows can be created using the electron.BrowserWindow class. A simple main.js file might just wait for the application to be ready and open a window:
const {app, BrowserWindow} = require('electron')
  const path = require('path')
  const url = require('url')
  
  function createWindow () {
    // Create the browser window.
    win = new BrowserWindow({width: 800, height: 600})
  
    // and load the index.html of the app.
    win.loadURL(url.format({
      pathname: path.join(__dirname, 'index.html'),
      protocol: 'file:',
      slashes: true
    }))
  }
  
  app.on('ready', createWindow)
The main.js should create windows and handle all the system events your application might encounter. A more complete version of the above example might open developer tools, handle the window being closed, or re-create windows on macOS if the user clicks on the app’s icon in the dock.
const {app, BrowserWindow} = require('electron')
  const path = require('path')
  const url = require('url')
  
  // Keep a global reference of the window object, if you don't, the window will
  // be closed automatically when the JavaScript object is garbage collected.
  let win
  
  function createWindow () {
    // Create the browser window.
    win = new BrowserWindow({width: 800, height: 600})
  
    // and load the index.html of the app.
    win.loadURL(url.format({
      pathname: path.join(__dirname, 'index.html'),
      protocol: 'file:',
      slashes: true
    }))
  
    // Open the DevTools.
    win.webContents.openDevTools()
  
    // Emitted when the window is closed.
    win.on('closed', () => {
      // 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.
      win = null
    })
  }
  
  // This method will be called when Electron has finished
  // initialization and is ready to create browser windows.
  // Some APIs can only be used after this event occurs.
  app.on('ready', createWindow)
  
  // Quit when all windows are closed.
  app.on('window-all-closed', () => {
    // On macOS 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()
    }
  })
  
  app.on('activate', () => {
    // On macOS it's common to re-create a window in the app when the
    // dock icon is clicked and there are no other windows open.
    if (win === null) {
      createWindow()
    }
  })
  
  // In this file you can include the rest of your app's specific main process
  // code. You can also put them in separate files and require them here.
Finally the index.html is the web page you want to show:
<!DOCTYPE html>
  <html>
    <head>
      <meta charset="UTF-8">
      <title>Hello World!</title>
    </head>
    <body>
      <h1>Hello World!</h1>
      We are using node <script>document.write(process.versions.node)</script>,
      Chrome <script>document.write(process.versions.chrome)</script>,
      and Electron <script>document.write(process.versions.electron)</script>.
    </body>
  </html>

Running Your App

Once you’ve created your initial main.js, index.html, and package.json files, you can try your app by running npm start from your application’s directory.
Clone and run the code in this tutorial by using the electron/electron-quick-start repository. Note: Running this requires Git.
# Clone the repository
  $ git clone https://github.com/electron/electron-quick-start
  # Go into the repository
  $ cd electron-quick-start
  # Install dependencies
  $ npm install
  # Run the app
  $ npm start
For a list of boilerplates and tools to kick-start your development process, see the Boilerplates and CLIs documentation.
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