前端性能优化（2.1 代码分离——入口起点 entry point）

入口起点分离： 使用 entry 手动的分离代码。（配置多，并且有一些隐患，不建议使用）

project

webpack-demo
|- package.json
|- webpack.common.js
|- webpack.prod.js
|- webpack.dev.js
|- /dist
|- /src
  |- index.js
  |- another-module.js
|- /node_modules

another-module.js

import _ from 'lodash'
console.log(
  _.join(['Another', 'module', 'loaded!'], ' ')
)

index.js

import _ from 'lodash'
function component () {
  const element = document.createElement('div')
  element.innerHTML = _.join(['Hello', 'webpack'], ' ')
  return element
}

document.body.appendChild(component())

webpack.common.js

使用 optimization.splitChunks 防止重复模块

const path = require('path')
const HtmlWebpackPlugin = require('html-webpack-plugin')
const { CleanWebpackPlugin } = require('clean-webpack-plugin')
// 从 webpack v4 开始，移除了 CommonsChunkPlugin，取而代之的是 optimization.splitChunks
module.exports = {
  entry: {
    index: './src/index.js',
    another: './src/another-module.js'
  },
  output: {
    filename: '[name].bundle.js',
    path: path.resolve(__dirname, 'dist')
  },
  plugins: [
    new HtmlWebpackPlugin(),
    new CleanWebpackPlugin()
  ],
  optimization: {
    splitChunks: {
      /**
       * 1. async，默认值，表示异步引入的模块
       * 2. initial，同步引入的模块
       * 3. all，两者皆可
       */
      chunks: 'all'
    }
  }
}

webpack.dev.js

const {merge} = require('webpack-merge')
const common = require('./webpack.common')

module.exports = merge(common, {
  mode: 'development',
  devtool: 'inline-source-map',
  devServer: {
    contentBase: './dist',
    port: 3000,
    open: true
  }
})

webpack.prod.js

const {merge} = require('webpack-merge')
const common = require('./webpack.common')

module.exports = merge(common, {
  mode: 'development',
  devtool: 'inline-source-map',
  devServer: {
    contentBase: './dist',
    port: 3000,
    open: true
  }
})