前言

每次编译代码时，需要手动输入yarn run build，挺麻烦的，有没有自动编译的方式呢？还真有，如下三种：

自动编译方式

1. webpack’s Watch Mode 观察模式
2. webpack-dev-server web服务器
3. webpack-dev-middleware webpack中间件

观察模式

在package.json中添加观察模式的npm script脚本

"scripts": {
    "watch": "webpack --watch",
    "build": "webpack"
 }

启动：yarn run watch
优点：自动编译
缺点：需手动刷新浏览器

web服务器

添加web服务器插件
yarn add webpack-dev-server -D
在package.json中添加web服务器的npm script脚本

"scripts": {
    "watch": "webpack --watch",
    "build": "webpack",
    "dev": "webpack-dev-server --open"
 }

在webpack.config.js配置文件中添加devServer配置项

const path = require('path')
const HtmlWebpackPlugin = require('html-webpack-plugin')
const CleanWebpackPlugin = require('clean-webpack-plugin')
const ManifestPlugin = require('webpack-manifest-plugin')

const HOST = process.env.HOST
const PORT = process.env.PORT && Number(process.env.PORT)

module.exports = {
  // 多入口，根据入口起点名称动态生成bundle名称
  entry: {
    app: './src/index.js',
    print: './src/print.js'
  },
  // 开发服务器，实时重新加载
  devServer: {
    contentBase: './dist'
  },
  plugins: [
    // 每次构建前清理dist文件夹
    new CleanWebpackPlugin(['dist']),
    // html-webpack-plugin插件默认生成index.html文件
    new HtmlWebpackPlugin({
      title: 'Document'
    })
  ],
  output: {
    filename: '[name].bundle.js',
    path: path.resolve(__dirname, 'dist')
  }
}

启动：yarn run dev
优点：自动编译+实时重新加载浏览器

webpack中间件

添加webpack中间件和express
yarn add express webpack-dev-middleware -D
在package.json中添加web服务器的npm script脚本

"scripts": {
    "watch": "webpack --watch",
    "build": "webpack",
    "dev": "webpack-dev-server --open",
    "server": "node server.js"
 }

webpack.config.js

const path = require('path')
const HtmlWebpackPlugin = require('html-webpack-plugin')
const CleanWebpackPlugin = require('clean-webpack-plugin')
const ManifestPlugin = require('webpack-manifest-plugin')

const HOST = process.env.HOST
const PORT = process.env.PORT && Number(process.env.PORT)

module.exports = {
  // 多入口，根据入口起点名称动态生成bundle名称
  entry: {
    app: './src/index.js',
    print: './src/print.js'
  },
  plugins: [
    // 每次构建前清理dist文件夹
    new CleanWebpackPlugin(['dist']),
    // html-webpack-plugin插件默认生成index.html文件
    new HtmlWebpackPlugin({
      title: 'Output Management'
    })
  ],
  output: {
    filename: '[name].bundle.js',
    path: path.resolve(__dirname, 'dist'),
    // 输出解析文件的目录
    publicPath: '/'
  }
}

server.js  启动服务器

const express = require('express')
const webpack = require('webpack')
const webpackDevMiddleware = require('webpack-dev-middleware')

const app = express()
const config = require('./webpack.config.js')
const compiler = webpack(config)

// 告诉express使用webpack中间件和webpack配置文件
app.use(webpackDevMiddleware(compiler, {
  publicPath: config.output.publicPath
}))

app.listen(8080, () => {
  console.log('listening on port 8080\n')
})

启动：yarn run server
优点：自动编译
缺点：需手动刷新浏览器+配置文件和插件多

总结

1. 观察模式在开发中不实用
2. web服务器力压群雄，实用性强，强烈推荐，vue-cli搭建以webpack搭建的模板就是使用web服务器
3. webpack中间件+express，使用2个插件，2个配置文件（webpack.config.js+server.js），配置复杂。