前端性能优化（2.3 preload prefetch 和 懒加载）

index.js

async function getComponent () {
  const { default: _ } = await import(/*webpackChunkName: "lodash"*/'lodash')
  await import(/* webpackChunkName: "style" */ './style.css')
  const element = document.createElement('div')
  element.innerHTML = _.join(['Hello', 'webpack'], ' ')
  const br = document.createElement('br')
  const btn = document.createElement('button')
  btn.innerHTML = 'Click me and look at the console'
  btn.onclick = e => import(/*webpackChunkName: "print" */ "./print").then(({ default: print }) => {
    print()
  })

  element.appendChild(br)
  element.appendChild(btn)

  return element
}
getComponent().then(component => {
  document.body.appendChild(component)
})

print.js

console.log('Print module loaded!')
export default () => {
  console.log('Button clicked!')
}

webpack.common.js

const path = require('path')
const HtmlWebpackPlugin = require('html-webpack-plugin')
const { CleanWebpackPlugin } = require('clean-webpack-plugin')
const PreloadWebpackPlugin = require('@vue/preload-webpack-plugin')
const MiniCssExtractPlugin = require('mini-css-extract-plugin')
module.exports = {
  entry: {
    index: './src/index.js',
  },
  output: {
    filename: '[name].bundle.js',
    path: path.resolve(__dirname, 'dist')
  },
  module: {
    rules: [
      {
        test: /.css$/,
        use: [MiniCssExtractPlugin.loader, 'css-loader']
      }
    ]
  },
  plugins: [
    new HtmlWebpackPlugin(),
    new CleanWebpackPlugin(),
    new PreloadWebpackPlugin(),
    new MiniCssExtractPlugin()
  ]
}

preload和prefetch的多页面配置

假设存在四个页面： index.html, book.html, content.html. search.html

new HtmlWebpackPlugin({
  title: 'index',
  template: './src/pages/index/index.html',
  filename: 'index.html',
  chunks: ['index'] // 标识页面chunk
}),
new HtmlWebpackPlugin({
  title: 'book',
  template: './src/pages/book/book.html',
  filename: 'book.html',
  chunks: ['book']
}),
new HtmlWebpackPlugin({
  title: 'content',
  template: './src/pages/content/content.html',
  filename: 'content.html',
  chunks: ['content']
}),
new HtmlWebpackPlugin({
  title: 'search',
  template: './src/pages/search/search.html',
  filename: 'search.html',
  chunks: ['search']
}),
new PreloadWebpackPlugin({
  rel: 'preload',
  excludeHtmlNames: ['book.html', 'content.html', 'search.html'],
  include: ['index'] // index preload本页面的
}),
new PreloadWebpackPlugin({
  rel: 'prefetch',
  excludeHtmlNames: ['book.html', 'content.html', 'search.html'],
  include: ['book'] // book prefetch index页面
}),
new PreloadWebpackPlugin({
  rel: 'preload',
  excludeHtmlNames: ['index.html', 'content.html', 'search.html'],
  include: ['book'] // book preload 本页面
}),
new PreloadWebpackPlugin({
  rel: 'prefetch',
  excludeHtmlNames: ['index.html', 'content.html', 'search.html'],
  include: ['content'] // content prefetch book 页面
}),
new PreloadWebpackPlugin({
  rel: 'preload',
  excludeHtmlNames: ['index.html', 'book.html', 'search.html'],
  include: ['content'] // content preload 本页面
}),
new PreloadWebpackPlugin({
  rel: 'preload',
  excludeHtmlNames: ['index.html', 'book.html', 'content.html'],
  include: ['search'] // search preload 本页面
})