一、什么是服务端渲染

客户端请求服务器，服务器根据请求地址获得匹配的组件，在调用匹配到的组件返回Promise (官方是asyncData方法)来将需要的数据拿到。最后再通过window.__initial_state=data将其写入网页，最后将服务端渲染好的网页返回回去。接下来客户端将用新的store状态把原来的store状态替换掉，保证客户端和服务端的数据同步。遇到没被服务端渲染的组件，再去发异步请求拿数据。

二、服务端渲染的环境搭建

这是vue官网的服务端渲染的示意图，ssr有两个入口文件，分别是客户端的入后文件和服务端的入口文件，webpack通过两个入口文件分别打包成给服务端用的server bundle和给客户端用的client bundle.当服务器接收到了来自客户端的请求之后，会创建一个渲染器bundleRenderer，这个bundleRenderer会读取上面生成的server bundle文件，并且执行它的代码， 然后发送一个生成好的html到浏览器，等到客户端加载了client bundle之后，会和服务端生成的DOM进行Hydration(判断这个DOM和自己即将生成的DOM是否相同，如果相同就将客户端的vue实例挂载到这个DOM上)
实现步骤：

1、创建vue实例（main.js）

importVuefrom'vue'
importAppfrom'./App.vue'
importiViewfrom'iview';
import{createStore}from'./store'
import{createRouter}from'./router'
import{sync}from'vuex-router-sync'
Vue.use(iView);
export functioncreateApp() {
conststore = createStore()
constrouter = createRouter()
sync(store,router)
constapp =newVue({
router,
store,
render: h => h(App)
})
return{app,router,store}
}

因为要做服务端渲染，所以这里不需要再用el去挂载，现将app、router、store导出

2、服务端入口文件（entry-server.js）

import{ createApp }from'./main'
constisDev = process.env.NODE_ENV !=='production'
const{ app,router,store } = createApp()
constgetAllAsyncData=function(component){
letstores = []
functionloopComponent(component) {
if(typeofcomponent.asyncData !=='undefined') {
for(letaofcomponent.asyncData({store,route: router.currentRoute})) {
stores.push(a)
}
}
if(typeofcomponent.components !=='undefined') {
for(letcincomponent.components){
loopComponent(component.components[c])
}
}
}
loopComponent(component)
returnstores
}
export defaultcontext => {
return newPromise((resolve,reject) => {
consts = isDev && Date.now()
const{url} = context
constfullPath = router.resolve(url).route.fullPath
if(fullPath !== url) {
reject({url: fullPath })
}
router.push(url)
router.onReady(() => {
constmatchedComponents = router.getMatchedComponents()
if(!matchedComponents.length) {
reject({code:404})
}
letallAsyncData = getAllAsyncData(matchedComponents[0])
Promise.all(allAsyncData).then(() => {
isDev && console.log(`data pre-fetch:${Date.now() - s}ms`)
context.state = store.state
resolve(app)
}).catch(reject)
},reject)
})
}

这个文件的主要工作是接受从服务端传递过来的context参数，context包含当前页面的url，用getMatchedComponents方法获取当前url下的组件，返回一个数组，遍历这个数组中的组件，如果组件有asyncData钩子函数，则传递store获取数据，最后返回一个promise对象。
context.state =
store.state的作用是将服务端获取到的数据挂载到context对象上，后面在server.js文件里会把这些数据直接发送到浏览器端与客户端的vue实例进行数据(状态)同步。

3、客户端入口文件（entry-client.js）

importVuefrom'vue'
import'es6-promise/auto'
import{ createApp }from'./main'
importProgressBarfrom'./components/ProgressBar.vue'
// global progress bar
constbar = Vue.prototype.$bar =newVue(ProgressBar).$mount()
document.body.appendChild(bar.$el)
Vue.mixin({
beforeRouteUpdate(to,from,next) {
const{ asyncData } =this.$options
if(asyncData) {
Promise.all(asyncData({
store:this.$store,
route: to
})).then(next).catch(next)
}else{
next()
}
}
})
const{ app,router,store } = createApp()
if(window.__INITIAL_STATE__) {
store.replaceState(window.__INITIAL_STATE__)
}
router.onReady(() => {
router.beforeResolve((to,from,next) => {
constmatched = router.getMatchedComponents(to)
constprevMatched = router.getMatchedComponents(from)
letdiffed =false
constactivated = matched.filter((c,i) => {
returndiffed || (diffed = (prevMatched[i] !== c))
})
constasyncDataHooks = activated.map(c => c.asyncData).filter(_ => _)
if(!asyncDataHooks.length) {
returnnext()
}
bar.start()
Promise.all(asyncDataHooks.map(hook => hook({ store,route: to })))
.then(() => {
bar.finish()
next()
})
.catch(next)
})
app.$mount('#app')
})
if('https:'=== location.protocol && navigator.serviceWorker) {
navigator.serviceWorker.register('/service-worker.js')
}

if(window.INITIAL_STATE) {
store.replaceState(window.INITIAL_STATE)
}
这句的作用是如果服务端的vuex数据发生改变，就将客户端的数据替换掉，保证客户端和服务端的数据同步
Service Worker主要用于拦截并修改访问和资源请求，细粒度地缓存资源。它运行浏览器在后台，运行环境与普通页面脚本不同，所以不能直接参与页面交互。出于安全考虑，service worker只能运行在HTTPS上，防止被人从中攻击。

4、创建服务端渲染器（server.js）

constfs = require('fs')
constpath = require('path')
constLRU = require('lru-cache')
constexpress = require('express')
constcompression = require('compression')
constresolve= file => path.resolve(__dirname,file)
const{ createBundleRenderer } = require('vue-server-renderer')
constisProd = process.env.NODE_ENV ==='production'|| process.env.NODE_ENV ==='beta'
constuseMicroCache = process.env.MICRO_CACHE !=='false'
constserverInfo =
`express/${require('express/package.json').version}`+
`vue-server-renderer/${require('vue-server-renderer/package.json').version}`
constapp = express()
consttemplate = fs.readFileSync(resolve('./src/index.template.html'),'utf-8')
functioncreateRenderer(bundle,options) {
returncreateBundleRenderer(bundle,Object.assign(options,{
template,
cache: LRU({
max:1000,
maxAge:1000*60*15
}),
basedir: resolve('./dist'),
runInNewContext:false
}))
}
letrenderer
letreadyPromise
if(isProd) {
constbundle = require('./dist/vue-ssr-server-bundle.json')
constclientManifest = require('./dist/vue-ssr-client-manifest.json')
renderer = createRenderer(bundle,{
clientManifest
})
}else{
readyPromise = require('./build/setup-dev-server')(app,(bundle,options) => {
renderer = createRenderer(bundle,options)
})
}
constserve= (path,cache) => express.static(resolve(path),{
maxAge: cache && isProd ?1000*60*60*24*30:0
})
app.use(compression({threshold:0}))
app.use('/dist',serve('./dist',true))
app.use('/static',serve('./static',true))
app.use('/service-worker.js',serve('./dist/service-worker.js'))
constmicroCache = LRU({
max:100,
maxAge:1000
})
constisCacheable= req => useMicroCache
functionrender(req,res) {
consts = Date.now()
res.setHeader("Content-Type","text/html")
res.setHeader("Server",serverInfo)
consthandleError= err => {
if(err.url) {
res.redirect(err.url)
}else if(err.code ===404) {
res.status(404).end('404 | Page Not Found')
}else{
// Render Error Page or Redirect
res.status(500).end('500 | Internal Server Error')
console.error(`error during render :${req.url}`)
console.error(err.stack)
}
}
constcacheable = isCacheable(req)
if(cacheable) {
consthit = microCache.get(req.url)
if(hit) {
if(!isProd) {
console.log(`cache hit!`)
}
returnres.end(hit)
}
}
constcontext = {
title:'Vue DB',// default title
url: req.url
}
renderer.renderToString(context,(err,html) => {
if(err) {
returnhandleError(err)
}
res.end(html)
if(cacheable) {
microCache.set(req.url,html)
}
if(!isProd) {
console.log(`whole request:${Date.now() - s}ms`)
}
})
}
app.get('*',isProd ? render : (req,res) => {
readyPromise.then(() => render(req,res))
})
constport = process.env.PORT ||8888
app.listen(port,() => {
console.log(`server started at localhost:${port}`)
})

5、客户端api文件create-api-client.js

/**
 * Created by lin on 2017/8/25.
 */

import axios from 'axios';
let api;

axios.defaults.baseURL = process.env.API_URL;
axios.defaults.timeout = 10000;

axios.interceptors.response.use((res) => {
  if (res.status >= 200 && res.status < 300) {
    return res;
  }
  return Promise.reject(res);
}, (error) => {
  return Promise.reject({message: '网络异常，请刷新重试', err: error});
});

if (process.__API__) {
  api = process.__API__;
} else {
  api = {
    get: function(url) {
      return new Promise((resolve, reject) => {
        axios.get(url).then(res => {
          resolve(res);
        }).catch((error) => {
          reject(error);
        });
      });
    },
    post: function(target, options = {}) {
      return new Promise((resolve, reject) => {
        axios.post(target, options).then(res => {
          resolve(res);
        }).catch((error) => {
          reject(error);
        });
      });
    }
  };
}

export default api;

6、服务端api文件create-api-server.js

/**
 * Created by lin on 2017/8/25.
 */

import axios from 'axios';
let cook = process.__COOKIE__ || '';
let api;

axios.defaults.baseURL = 'https://api.douban.com/v2/';
axios.defaults.timeout = 10000;

axios.interceptors.response.use((res) => {
  if (res.status >= 200 && res.status < 300) {
    return Promise.resolve(res);
  }
  return Promise.reject(res);
}, (error) => {
  // 网络异常
  return Promise.reject({message: '网络异常，请刷新重试', err: error, type: 1});
});

if (process.__API__) {
  api = process.__API__;
} else {
  api = {
    get: function(target) {
      return new Promise((resolve, reject) => {
        axios.request({
          url: encodeURI(target),
          method: 'get',
          headers: {
            'Cookie': cook
          }
        }).then(res => {
          resolve(res);
        }).catch((error) => {
          reject(error);
        });
      });
    },
    post: function(target, options = {}) {
      return new Promise((resolve, reject) => {
        axios.request({
          url: target,
          method: 'post',
          headers: {
            'Cookie': cook
          },
          params: options
        }).then(res => {
          resolve(res);
        }).catch((error) => {
          reject(error);
        });
      });
    }
  };
}

export default api;

三、注意事项

问题：window is not defined

答：给用到浏览器对象的地方加if (typeof window !== 'undefined') {}，有一些插件里也用到了浏览器对象，在使用的地方也加一个条件判断：

if (typeofwindow !== 'undefined') {
Vue.use(VueAnalytics, {
id: process.env.UA_TRACKING_ID,
router
})
}

问题：用到非Vue系列的插件，如hello.all.js(三方登录的插件)，需要用的地方才引用，报的错和问题1一样。

答：这个时候不能再用import导入，需要使用require，

let hello
if (typeof window !== 'undefined') {
hello = require('hello')
}

问题：引用bootstrap

答：将bootstrap.css和bootstrap.js加入webpack.base.config.js的entry中的vendor中

问题：bootstap需要jquery，此时把jQuery加在vendor中没用。

答：给webpack.base.config.js的plugins添加一个插件，如：

newwebpack.ProvidePlugin({
$ : "jquery",
jQuery : "jquery",
"window.jQuery" :"jquery"
})

四、例子

git地址：https://github.com/LRithe/ssr-vue
这是一个服务端渲的例子