Webpack 热更新与自动刷新浏览器原理深度解析

npm i webpack webpack-cli -D
npm i webpack-dev-server -D
npm i html-webpack-plugin -D

# 启动开发服务器
webpack serve --mode development --config webpack.config.js

// pkg.json
{
"scripts": {
"dev": "webpack serve --mode development --config webpack.config.js",
"build": "webpack build --mode production --config webpack.config.js"
},
"devDependencies": {
"webpack": "^5.45.1",
"webpack-cli": "^4.7.2",
"webpack-dev-server": "^3.11.2",
"html-webpack-plugin": "^5.3.2",
}
}

// webpack.config.js
const path = require('path')
const HtmlWebpackPlugin = require('html-webpack-plugin')

module.exports = {
entry: './src/index.js',
output: {
filename: 'main.js',
path: path.resolve(__dirname, 'dist'),
},
devServer: {
hot: true, // 开启热更新
port: 8080, // 指定服务器端口号
},
plugins: [
new HtmlWebpackPlugin({
template: './index.html'
})
]
}

// node_modules/webpack-dev-server/bin/webpack-dev-server.js

const webpack = require('webpack');

const config = require('../../webpack.config');

const Server = require('../lib/Server')



const compiler = webpack(config);

const server = new Server(compiler);

server.listen(8080, 'localhost', () => {})

// node_modules/webpack-dev-server/lib/Server.js

class Server {

constructor() {

this.setupApp();

this.createServer();

}

//创建http应用

setupApp() {

this.app = express();

}

//创建http服务

createServer() {

this.server = http.createServer(this.app);

}

//监听端口号

listen(port, host, callback) {

this.server.listen(port, host, callback)

this.createSocketServer();

}

//基于http服务创建websocket服务，并注册监听事件connection

createSocketServer() {

const io = socketIO(this.server);

io.on('connection', (socket) => {

this.clientSocketList.push(socket);

socket.emit('hash', this.currentHash);

socket.emit('ok');

socket.on('disconnect', () => {

let index = this.clientSocketList.indexOf(socket);

this.clientSocketList.splice(index, 1)

})

})

}

}



module.exports = Server;

//监听编译完成，当编译完成后通过websocket向浏览器发送广播

setupHooks() {

let { compiler } = this;

compiler.hooks.done.tap('webpack-dev-server', (stats) => {

this.currentHash = stats.hash;

this.clientSocketList.forEach((socket) => {

socket.emit('hash', this.currentHash);

socket.emit('ok');

})

})

}

// node_modules/webpack-dev-middleware/index.js

const MemoryFs = require('memory-fs')

compiler.watch({}, () => {})

let fs = new MemoryFs();

this.fs = compiler.outputFileSystem = fs;

//node_modules/webpack-dev-server/lib/utils/updateCompiler.js

const path = require('path');

function updateCompiler(compiler) {

compiler.options.entry = {

main: [

path.resolve(__dirname, '../../client/index.js'),

path.resolve(__dirname, '../../../webpack/hot/dev-server.js'),

config.entry,

]

}

}

module.exports = updateCompiler

let currentHash;

let hotEmitter = new EventEmitter();

const socket = window.io('/');



socket.on('hash', (hash) => {

currentHash = hash;

})

socket.on('ok', () => {

reloadApp();

})



function reloadApp() {

hotEmitter.emit('webpackHotUpdate', currentHash)

}

let lastHash;

hotEmitter.on('webpackHotUpdate', (currentHash) => {

if (!lastHash) {

lastHash = currentHash;

return;

}

module.hot.check();

})