Detailed explanation of the use of dev-server.js configuration file of vue-cli scaffolding-JS Tutorial-php.cn

This time I will bring you the dev-server.js of vue-cli scaffoldingConfiguration fileDetailed explanation of usage, Note on using vue-cli scaffolding dev-server.js configuration file What are the matters ? Below are actual cases, let’s take a look at them.

This article systematically explains the dev-server.js configuration file in the vue-cli scaffolding build directory

1. This configuration file is the entry configuration file for the commands npm run dev and npm run start. It is mainly used in the development environment

2. Since this is a system configuration file and will involve many modules and plug-ins, I will explain this part in multiple articles. Please pay attention to other articles on my blog

3. About comments •When it comes to more complex explanations, I will write the explanations to a separate comment module through identification (such as (1)), please check it yourself

4. Upload the code

// 导入check-versions.js文件，并且执行导入的函数，用来确定当前环境node和npm版本是否符合要求
// 关于check-versions请查看我博客check-versions的相关文章
require('./check-versions')()
// 导入config目录下的index.js配置文件，此配置文件中定义了生产和开发环境中所要用到的一些参数
// 关于index.js的文件解释请看我博客的index.js的相关文章
var config = require('../config')
// 下面表示如果如果没有定义全局变量NODE_ENV，则将NODE_ENV设置为"development"
if (!process.env.NODE_ENV) {
  process.env.NODE_ENV = JSON.parse(config.dev.env.NODE_ENV)
}
// opn插件是用来打开特定终端的，此文件用来在默认浏览器中打开链接 opn(url)
var opn = require('opn')
// nodejs路径模块
var path = require('path')
// nodejs开发框架express，用来简化操作，有兴趣可以自行去了解
var express = require('express')
// 引入webpack模块，用来使用webpack内置插件
var webpack = require('webpack')
// 引入http-proxy-middleware插件，此插件是用来代理请求的只能用于开发环境，目的主要是解决跨域请求后台api
var proxyMiddleware = require('http-proxy-middleware')
// 下面的意思是指，如果不是testing环境就引入webpack.dev.conf.js配置文件
// 关于webpack.dev.conf.js配置文件请关注我的相关文章，建议现在就去看，否则后面看着吃力
var webpackConfig = process.env.NODE_ENV === 'testing' ?
  require('./webpack.prod.conf') :
  require('./webpack.dev.conf')
// default port where dev server listens for incoming traffic
// 下面是webpack-dev-server 监听的端口号，因为没有设置process.env.PORT，所以下面监听的就是config.dev.port即8080
var port = process.env.PORT || config.dev.port
  // automatically open browser, if not set will be false
// 下面是true,至于为啥，本来就是true还要加!!两个感叹号，估计是vue作者装了个逼吧
var autoOpenBrowser = !!config.dev.autoOpenBrowser
  // Define HTTP proxies to your custom API backend
  // https://github.com/chimurai/http-proxy-middleware
// 下面是解决开发环境跨域问题的插件，我在config目录index.js文章中有介绍，自行查看
var proxyTable = config.dev.proxyTable
// 下面是创建node.js的express开发框架的实例，别问我为什么这样，自己看node.js去吧
var app = express()
// 把配置参数传递到webpack方法中，返回一个编译对象，这个编译对象上面有很多属性，自己去看吧，主要是用到里面的状态函数 如compilation，compile，after-emit这类的
var compiler = webpack(webpackConfig)
// 下面是webpack-dev-middleware和webpack-hot-middleware两兄弟，这两个是黄金组合
// 而vue作者用这两个插件也是用的最基本的形式，详情看(1) (2)
var devMiddleware = require('webpack-dev-middleware')(compiler, {
  publicPath: webpackConfig.output.publicPath,
  quiet: true // 使用friendly-errors-webpack-plugin插件这个必须设置为true，具体看我的wepback-dev-config.js
})
var hotMiddleware = require('webpack-hot-middleware')(compiler, {
    log: () => {} // 使用friendly-errors-webpack-plugin插件这个必须设置为true，具体看我的wepback-dev-config.js
  })
  // force page reload when html-webpack-plugin template changes
compiler.plugin('compilation', function(compilation) {
  // webpack任何一个插件都plugin这个方法，里面可以传递钩子函数，用来在插件各个阶段做特殊处理，钩子函数种类很多
  compilation.plugin('html-webpack-plugin-after-emit', function(data, cb) {
    // 当插件html-webpack-plugin产出完成之后，强制刷新浏览器
    hotMiddleware.publish({ action: 'reload' })
    cb()
  })
})
// proxy api requests
Object.keys(proxyTable).forEach(function(context) {
  // 下面是代理表的处理方法，看看就行了，几乎用不上，除非你是全栈，不用webpack-dev-server，使用后台语言做服务器
  var options = proxyTable[context]
  if (typeof options === 'string') {
    options = { target: options }
  }
  app.use(proxyMiddleware(options.filter || context, options))
})
// handle fallback for HTML5 history API
// 这个插件是用来解决单页面应用，点击刷新按钮和通过其他search值定位页面的404错误
// 详情请看(3)
app.use(require('connect-history-api-fallback')())
// serve webpack bundle output
// app.use是在响应请求之前执行的，用来指定静态路径，挂载静态资源
app.use(devMiddleware)
// enable hot-reload and state-preserving
// compilation error display
app.use(hotMiddleware)
// serve pure static assets
// 下面的staticPath是 static ，path.posix.join其他配置文件中我已经介绍了，这里不再赘述
var staticPath = path.posix.join(config.dev.assetsPublicPath, config.dev.assetsSubDirectory)
// 挂载静态资源，下面的方法是用虚拟目录来访问资源，staticPath就是虚拟目录路径，其实不管设不设置都是static
app.use(staticPath, express.static('./static'))
// 下面结果就是 'http://localhost:8080'
var uri = 'http://localhost:' + port
// 下面是es6的promise规范，用来处理嵌套请求的
var _resolve
var readyPromise = new Promise(resolve => {
  _resolve = resolve // resolve是一个回调函数专门用来传递成功请求的数据
})
// 下面是加载动画
console.log('> Starting dev server...')
// waitUntilValid是webpack-dev-middleware实例的方法，在编译成功之后调用
devMiddleware.waitUntilValid(() => {
  console.log('> Listening at ' + uri + '\n')
    // when env is testing, don't need open it
    // 测试环境不打开浏览器
  if (autoOpenBrowser && process.env.NODE_ENV !== 'testing') {
    opn(uri)
  }
  _resolve() // 这里没有传递数据，这只是在模拟
})
// node.js监听端口
var server = app.listen(port)
// 这个导出对象是用来对外提供操作服务器和接受数据的接口，vue作者可谓考虑颇深啊
module.exports = {
  ready: readyPromise, // promise实例，可以通过readyPromise.then收到数据
  close: () => {
    server.close() // 关闭服务器
  }
}

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explain

(1)webpack-dev-middleware plug-in

This plug-in can only be used in the development environment. The following is an explanation of this plug-in

This is a simple webpack packagingmiddleware. This plug-in mainly does one thing for files, that is, when the files are modified, they are submitted to the webpack server and then process these modified files

This plug-in has several advantages

First, all files are written on disk, and file processing is performed in memory

Second, if the file is changed in watch mode, this middleware will not serve these old bundles. If there are file changes on these old bundles, this middleware will not send the request, but wait until the current compilation Ended, the request will be sent only when the latest file has been changed, so you don’t need to refresh it manually

Third, I will optimize

in future versions In summary, this middleware is the core of webpack-dev-server, which implements the function of modifying files and automatically refreshing webapack

Install npm install webpack-deb-middleware --save-dev

The usage method is as follows. The following usage method is also the code implemented by webpack-dev-server

var webpackMiddleware = require("webpack-deb-middleware");
app.use(webpackMiddleware(webpack({obj1}),{obj2}))

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app.use is express’s method, used to set static paths

The above obj1 is the webpack configuration object, which is converted into a compiler object using the webpack method. The obj2 configuration is the configuration after the updated file is packaged, using

After webpackMiddleware processes it, it returns a static path, which is convenient for obtaining the configuration items of obj2 in the file. You can check it by yourself. You must add publicPath

Having said that, I won’t give it away. In short, our static server is node.js. Now the file has been modified. After webpack-dev-middleware compiles the modified file, it tells the nodejs server which files have been modified and the latest File upload to the static server, that’s clear enough

(2)webpack-hot-middleware plug-in

This plug-in is used to notify the browser of the updated files compiled by webpack-dev-middleware, and tell the browser how to update the files, thereby realizing Webpack hot reloading

By using these two plug-ins together, you don't need webpack-dev-sever, that is, you can implement the hot-replacement function by yourself. The webpack-hot-middleware plug-in notifies the browser to update files roughly through a json object. I won’t go into details about the specific implementation mechanism here. Let’s look at the specific usage

Install npm install webpack-hot-middleware --save-dev

After using webpack-dev-middleware, add the following code

app.use(require("webpack-hot-middleware")(compiler));

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(3)connect-history-api-fallback plug-in

Because when developing a single-page application, the project is generally one page. If you click the refresh button and the link does not refer to the address of the homepage, it will 404; or if I use other links such as /login.html But if there is no login.html, an error will be reported, and the function of this plug-in is to position the page to the default index.html when there is an improper operation that causes 404. It is also relatively simple to use, just remember to use it this way.

Install npm install --save connect-history-api-fallback

Use

var history = require('connect-history-api-fallback');
  var express = require('express');
  var app = express();
  app.use(history());

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I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the php Chinese website!