前端工程化开发的一个重要标志就是热替换技术，它大大的提高开发效率，使我们专注于写代码，webpack2中的热替换相比较1更加简洁。

1. 先看效果

Demo地址 https://github.com/leinov/react-hmr-demo

2.目录结构

3.项目目录结构文件描述

• bin 执行文件
• node_modules node包

• public 静态资源文件

  static 静态资源
  dist 编译后文件

• src 项目js文件
• .bablrc babel配置文件
• webpack.config.dev.js开发模式webpack配置

• webpack.config.pro.js生产模式webpack配置

3.技术依赖

• node
• react
• babel
• ES6/ES2015
• react-hmre

• webpack

  babel-loader,css-loader,sass-loader,style-loader,webpack-hot-middleware,webpack-hot-middleware

热加载最重要的几个配置是packge.json/devserver.js/webpack.config.dev.js/webpack.config.prod.js/.babelrc

packge.json

{
  "name": "react-hmr-demo",
  "version": "1.0.0",
  "description": "react-hmr-demo",
  "main": "index.js",
  "scripts": {
    "dev": "node bin/devserver.js",
    "build":" webpack --config webpack.config.prod.js ",
    "start":"node bin/server.js"
  },
  "repository": {
    "type": "git",
    "url": "git+https://github.com/leinov/react-hmr-demo.git"
  },
  "author": "leinov",
  "license": "ISC",
  "dependencies": {
    "express": "^4.15.4",
    "react": "^15.6.1",
    "react-dom": "^15.6.1"
  },
  "devDependencies": {
    "babel-core": "^6.26.0",
    "babel-loader": "^7.1.2",
    "babel-polyfill": "^6.26.0",
    "babel-preset-es2015": "^6.24.1",
    "babel-preset-react": "^6.24.1",
    "babel-preset-react-hmre": "^1.1.1",
    "css-loader": "^0.28.5",
    "eventsource-polyfill": "^0.9.6",
    "node-sass": "^4.5.3",
    "sass-loader": "^6.0.6",
    "style-loader": "^0.18.2",
    "webpack": "^3.5.5",
    "webpack-dev-middleware": "^1.12.0",
    "webpack-hot-middleware": "^2.18.2"
  }
}

scripts的几个命令

$ npm run dev //开发模式

$ npm run build //编译打包

npm start //正式环境运行

webpack.config.dev.js

var path = require('path');
var webpack = require('webpack');
 
module.exports = {

    devtool: 'cheap-module-eval-source-map',//打包构建信息
    
    entry: [

        'eventsource-polyfill',//for IE
        'webpack-hot-middleware/client',//webpack服务连接到浏览器接收更新
        
        './src/index.js'
    ],
    
    output: {
        filename: 'boundle.js',
        publicPath: '/dist/js/' 
    },
    
    module: {

        loaders: [{
                test: /\.js$/,
                loaders: ['babel-loader'],
                exclude: /node_modules/ //哪些文件下的需要用到babel
            }, {
                test: /\.css$/,
                loaders: ['style-loader', 'css-loader'],
            },
            {
                test: /\.scss$/, 'css-loader', 'sass-loader'],
            {
                test: /\.(png|jpg|gif)$/,
                loaders: ['url?limit=8192&name=images/[name].[ext]'],
            }
        ]
    } ,
    
    resolve:{
    
        alias: {
        
            css: path.resolve(__dirname, 'public/static/css/'), //css目录别名
        }
    },
    
    plugins: [
    
        new webpack.HotModuleReplacementPlugin(),//热替换插件
        new webpack.NoEmitOnErrorsPlugin()
    ]
};

.babelrc

{
  "presets": ["react","es2015"]，
  "env": {
        "development": {
    
            "presets": ["react-hmre"]
        }
  }
}

devserver.js

var path = require('path');
var express = require('express');
var webpack = require('webpack');
var config = require('../webpack.config.dev');

var app = express();
var compiler = webpack(config);

var webpackDevMiddleware = require("webpack-dev-middleware");

app.use(webpackDevMiddleware(compiler,{

    noInfo: false,//true将打印编译信息（建议false，true会打印很多信息）
    publicPath: config.output.publicPath //绑定middleware
}));

var webpackHotMiddleware = require('webpack-hot-middleware');
app.use(webpackHotMiddleware(compiler));
 

app.get('*',function(req,res) {

    res.sendFile(path.resolve(__dirname,'../index.html')); //
});

app.listen(3100,function(err) {

    if (err) {
        console.log(err);
        return;
    }
    console.log('Listening at http://localhost:3100');
});

这样就可以实现热加载了，在项目根目录执行

$ npm run dev

webpack.config.prod.js

var path = require('path');
var webpack = require('webpack');

module.exports = {
    devtool: 'cheap-module-eval-source-map',entry: [
        './src/index.js'
    ],output: {

        path: path.join(__dirname,'public/dist/js'),filename: 'boundle.js',},module: {

        loaders: [{
                test: /\.js$/,loaders: ['babel-loader'],exclude: /node_modules/  
            },{
                test: /\.css$/,loaders: ['style-loader','css-loader'],{
                test: /\.scss$/,'css-loader','sass-loader'],{
                test: /\.(png|jpg|gif)$/,loaders: ['url?limit=8192&name=images/[name].[ext]'],}
        ]
    },resolve:{
        alias: {
            css: path.resolve(__dirname,'public/static/css/'),img: path.resolve(__dirname,'public/static/img/'),}
    },plugins: [
   
         new webpack.HotModuleReplacementPlugin(),new webpack.NoEmitOnErrorsPlugin(),new webpack.optimize.UglifyJsPlugin({
                 compress: {
                   warnings: false
               }
           })
          
       ]
    };

生产的webpack主要完成开发后的编译打包，在plugins里多了压缩插件,在项目根目录执行

$ npm run build

bin/server.js

生产环境启动文件

var path = require('path');
var express = require('express');
var app = express();
 
var oneYear = 60 * 1000 * 60 * 24 * 30;

app.use(express.static(path.resolve(__dirname,'../public'),{ maxAge: oneYear }));

app.get('*','../index.html'));
});

app.listen(3200,function(err) {

    if (err) {
        console.log(err);
        return;
    }
  console.log('Listening at http://localhost:3200');
  
});

$ npm start //运行生产环境

Demo地址 https://github.com/leinov/react-hmr-demo