webpack本身有dev和prodcution两套环境，我们的项目还有uat环境，只有两套环境并无法满足项目开发的需要，因为我参考webpack搭建dev环境的方式搭建了uat环境。
首先，找到项目的package.json,找到scripts,加上uat指令的定义，

"scripts": {
    "dev": "node build/dev-server.js",
    "start": "node build/dev-server.js",
    "uat": "node build/uat-server.js",    
    "build": "node build/build.js",
    "lint": "eslint --ext .js,.vue src"
  },

很容易理解，当我们执行npm run dev时候执行node中build目录的dev-server.js，所以我们定义了uat指令执行uat-server.js。

项目目录.png

uat-server.js

require('./check-versions')()

var config = require('../config')
if (!process.env.NODE_ENV) {
  process.env.NODE_ENV = JSON.parse(config.uat.env.NODE_ENV)
}

var opn = require('opn')
var path = require('path')
var express = require('express')
var webpack = require('webpack')
var proxyMiddleware = require('http-proxy-middleware')
var webpackConfig = require('./webpack.uat.conf')

// default port where uat server listens for incoming traffic
var port = process.env.PORT || config.uat.port
// automatically open browser, if not set will be false
var autoOpenBrowser = !!config.uat.autoOpenBrowser
// Define HTTP proxies to your custom API backend
// https://github.com/chimurai/http-proxy-middleware
var proxyTable = config.uat.proxyTable

var app = express()
var compiler = webpack(webpackConfig)

var devMiddleware = require('webpack-dev-middleware')(compiler, {
  publicPath: webpackConfig.output.publicPath,
  quiet: true
})

var hotMiddleware = require('webpack-hot-middleware')(compiler, {
  log: () => {},
  heartbeat: 2000
})
// force page reload when html-webpack-plugin template changes
compiler.plugin('compilation', function (compilation) {
  compilation.plugin('html-webpack-plugin-after-emit', function (data, cb) {
    hotMiddleware.publish({ action: 'reload' })
    cb()
  })
})

// proxy api requests
Object.keys(proxyTable).forEach(function (context) {
  var options = proxyTable[context]
  if (typeof options === 'string') {
    options = { target: options }
  }
  app.use(proxyMiddleware(options.filter || context, options))
})

// handle fallback for HTML5 history API
app.use(require('connect-history-api-fallback')())

// serve webpack bundle output
app.use(devMiddleware)

// enable hot-reload and state-preserving
// compilation error display
app.use(hotMiddleware)

// serve pure static assets
var staticPath = path.posix.join(config.uat.assetsPublicPath, config.uat.assetsSubDirectory)
app.use(staticPath, express.static('./static'))

var uri = 'http://localhost:' + port

var _resolve
var readyPromise = new Promise(resolve => {
  _resolve = resolve
})

console.log('> Starting uat server...')
devMiddleware.waitUntilValid(() => {
  console.log('> Listening at ' + uri + '\n')
  // when env is testing, don't need open it
  if (autoOpenBrowser && process.env.NODE_ENV !== 'testing') {
    opn(uri)
  }
  _resolve()
})

var server = app.listen(port)

module.exports = {
  ready: readyPromise,
  close: () => {
    server.close()
  }
}

webpack.uat.conf.js

var utils = require('./utils')
var webpack = require('webpack')
var config = require('../config')
var merge = require('webpack-merge')
var baseWebpackConfig = require('./webpack.base.conf')
var HtmlWebpackPlugin = require('html-webpack-plugin')
var FriendlyErrorsPlugin = require('friendly-errors-webpack-plugin')

// add hot-reload related code to entry chunks
Object.keys(baseWebpackConfig.entry).forEach(function (name) {
  baseWebpackConfig.entry[name] = ['./build/dev-client'].concat(baseWebpackConfig.entry[name])
})

module.exports = merge(baseWebpackConfig, {
  module: {
    rules: utils.styleLoaders({ sourceMap: config.uat.cssSourceMap })
  },
  // cheap-module-eval-source-map is faster for uat
  devtool: '#cheap-module-eval-source-map',
  plugins: [
    new webpack.DefinePlugin({
      'process.env': config.uat.env
    }),
    // https://github.com/glenjamin/webpack-hot-middleware#installation--usage
    new webpack.HotModuleReplacementPlugin(),
    new webpack.NoEmitOnErrorsPlugin(),
    // https://github.com/ampedandwired/html-webpack-plugin
    new HtmlWebpackPlugin({
      filename: 'index.html',
      template: 'index.html',
      inject: true
    }),
    new FriendlyErrorsPlugin()
  ]
})

uat.env.js

var merge = require('webpack-merge')
var prodEnv = require('./prod.env')

module.exports = merge(prodEnv, {
  NODE_ENV: '"uat"',
  API_ROOT: '"https://uat.xxx.com"',
})

找到config下方的index.js
在dev下方增加uat的配置，配置如下：

uat: {
    env: require('./uat.env'),
    port: 8080,
    autoOpenBrowser: true,
    assetsSubDirectory: 'static',
    assetsPublicPath: '/',
    proxyTable: {},
    // CSS Sourcemaps off by default because relative paths are "buggy"
    // with this option, according to the CSS-Loader README
    // (https://github.com/webpack/css-loader#sourcemaps)
    // In our experience, they generally work as expected,
    // just be aware of this issue when enabling this option.
    cssSourceMap: false
  }

这样，搭建了dev,uat和production三套环境，我们在dev.env.js增加API_ROOT：

var merge = require('webpack-merge')
var prodEnv = require('./prod.env')

module.exports = merge(prodEnv, {
  NODE_ENV: '"development"',
  API_ROOT: '"http://dev.xxx.com"',//根据项目情况配置，
})

在prod.env.js增加API_ROOT:

module.exports = {
  NODE_ENV: '"production"',
  API_ROOT: 'window.location.origin'
}

在配置api接口的文件中，将baseURL设置成：

axios.defaults.baseURL = process.env.API_ROOT;

这里以axios的设置为例，项目根据实际情况调整。
如此，当我们运行

npm run dev

指向的域名服务器是

API_ROOT: '"http://dev.xxx.com"',//根据项目情况配置，

当我们运行

 npm run uat

指向的域名服务器是

API_ROOT: '"https://uat.xxx.com"',

这是前面配置的自定义指令，可根据项目实际情况定义自己的指令
当我们运行

npm run build

指向的域名服务器是

  API_ROOT: 'window.location.origin'

打包项目的时候，打包的是根据服务器获取到相应的接口，我们就不用调来调去，也不容易出错，有问题欢迎留言讨论。