Explain in detail the issues related to implementing react server rendering

This article mainly introduces the detailed implementation of react server rendering from scratch. Now I will share it with you and give you a reference.

Preface

When I was writing koa recently, I thought, if part of my code provides API and part of the code supports SSR, how should I write it? (If you don’t want to split it into two services)
And I have also used some server-side rendering in the projects I wrote recently, such as nuxt, and I have also worked on next projects. It is true that the development experience is very friendly, but friendly is still friendly. , how is it implemented specifically? Have you ever considered it?

Based on a truth-seeking and pragmatic attitude, I chose react as the research object (mainly because Vue has been written a bit too much, which is disgusting). Then I will simply write a react server-side rendering demo at the minimum cost.

Technology stack used

react 16 webpack3 koa2

Let’s see how it implements server-side rendering, here we go!

Why use server-side rendering

Advantages

It’s nothing more than two points

1. SEO Friendly

2. Speed ​​up the first screen rendering and reduce the white screen time

Then the question is what is SEO

One sentence introduction is that most of the websites we make now are SPA websites. All pages and data come from ajax. When the search engine spider comes to collect the web pages, they find that they are all empty? So do you think the weight and effect of your website's inclusion are good or bad?

The core of our SEO optimization is also described in the following content:

The following is the key point!

Let the server return the HTML with content to us. If the event occurs, the browser will render it again for mounting.

Build the koa environment

New An ssr project, and initialize npm

mkdir ssr && cd ssr
npm init

In the following code, we use import jsx and other syntaxes, which are not supported by the node environment, so we need to configure babel

Create a new one in the current project Files app.js and index.js, and then

babel's entrance, the index.js code is as follows

require('babel-core/register')()

require('babel-polyfill')
require('./app')

The entrance of our project, the app.js code is as follows

import Koa from 'koa'
const app = new Koa()

// response
app.use((ctx) => {
 ctx.body = 'Hello Koa'
})

app.listen(3000)
console.log("系统启动，端口：3000")

root Create a new .babelrc file in the directory

The content is:

{
 "presets": ["react", "env"]
}

Install the dependencies required above

npm install babel-core babel-polyfill babel-preset-env babel-preset-react nodemon --save-dev
npm i koa --save

Configure the startup script

package.json

"scripts": {
 "dev": "nodemon index.js",
}

Here you run npm run dev and open localhost:3000

You will see hello Koa

Is it very simple to start a service

Install React

cnpm install react react-dom --save

Create a new app folder in the root directory, and create a new main.js in the folder

The main.js code is as follows

import React from 'react'

export default class Home extends React.Component {
 render () {
  return <p>hello world</p>
 }
}

Server.js before modification

import Koa from 'koa'
import React from 'react'
import { renderToString } from 'react-dom/server'
import App from './app/main'

const app = new Koa()

// response
app.use(ctx => {
 let str = renderToString(<App />)

 ctx.body = str
})

app.listen(3000)

console.log(&#39;系统启动，端口：8080&#39;)

At this time, npm run dev

You will see hello world appear on the screen

Open chrome developer The tool checks our request:

Our simplest react component becomes str and passed in

Here we use a method:

renderToString - In fact, it is to render the component into a string

So far, we have not added events and other interactive behaviors to the component. Let us try it next

Modify main .js code

import React from 'react'

export default class Home extends React.Component {
 render () {
  return <p onClick={() => window.alert(123)}>hello world</p>
 }
}

Refresh our page again, hey, is it useless?

That’s because the backend can only render the component into a string of html. Event binding and other things need to be executed on the browser side
So how do we bind the event?

Then you will definitely guess that since the server renders a string of html, the way to mount the event is to re-render it once in the browser

Just do it Do

Configure webpack

Create a new webpack.config.js under the root directory

The following is the content of webpack.config.js:

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

module.exports = {
 entry: {
  main: './app/index.js'
 },
 output: {
  filename: '[name].js',
  path: path.join(__dirname, 'public'),
  publicPath: '/'
 },
 resolve: {
  extensions: ['.js', '.jsx']
 },
 module: {
  loaders: [
   {test: /\.jsx?$/,
    loaders: ['babel-loader'],
   }
  ]
 }
}

The above configuration sets the entry to the app/index.js file

Then we will create one

The following is the code of app/index.js:

import Demo from './main'
import ReactDOM from 'react-dom'
import React from 'react'
ReactDOM.render(<Demo />, document.getElementById(&#39;root&#39;))

Because browser rendering needs to mount the root component to a certain dom node, we set an entrance for our react code

There is a problem at this time, that is, the document object node environment is not If it doesn't exist, how to solve it?

does not exist? If it doesn’t exist, then I don’t need it. The core of SSR is to return specific HTML content in the requested URL. I don’t care about events or anything like that, so I just return the root component directly to renderToString

.

Let’s modify our service code to support server rendering

Add some dependencies

cnpm i --save koa-static koa-views ejs

1. koa-static: In the middle of processing static files File

2. koa-views: middleware for configuring templates

3. ejs: a template engine

Modify the code of server.js

import Koa from 'koa'
import React from 'react'
import { renderToString } from 'react-dom/server'
import views from 'koa-views'
import path from 'path'

import Demo from './app/main'
const app = new Koa()
// 将/public文件夹设置为静态路径
app.use(require('koa-static')(__dirname + '/public'))
// 将ejs设置为我们的模板引擎
app.use(views(path.resolve(__dirname, './views'), { map: { html: 'ejs' } }))

// response
app.use(async ctx => {
 let str = renderToString(<Demo />)
 await ctx.render(&#39;index&#39;, {
  root: str
 })
})

app.listen(3000)

console.log(&#39;系统启动，端口：8080&#39;)

Create our rendering template below

Create a views folder

Create a new index.html in it:

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <base href="/client" rel="external nofollow" >
</head>
<body>
  <p id="root"><%- root %></p>
  <script src="/main.js"></script>
</body>
</html>

You can put some variables in this html, such as this c7f7f00800564bf33bc4d7d2fb90b606, which is where the renderToString result will be placed later.

/main.js is the code built by react

Let’s test our code directly

1. In package.json

新增：

 "scripts": {
  "dev": "nodemon index.js",
  "build": "webpack"
 },

2. 运行 npm run build， 构建出我们的react代码

3. npm run dev

点击一下代码，是不是会 alert(123)

 tada 撒花，恭喜你，一个最简单服务器渲染就已经完成

到这里核心的思想就都已经讲完了，总结来说就下面三点：

1. 起一个node服务

2. 把react 根组件 renderToString渲染成字符串一起返回前端

3. 前端再重新render一次

原理就是这么简单

但是具体开发的时候还会有各种各样的需求，比如：

1. 不可能我每次改完代码都重新构建看效果吧 => 需要 实时构建

2. create-react-app 都是热更新，你还要刷新是不是太蠢了 => 需要支持热更新

3. 其他一些配套的周边，如： react-router, redux 或者mobx怎么支持呢 => 需要完善的生态

.etc

这些问题都是用完 官方脚手架之后就回不去了的，所以更多的配置可以参考下面的repo（是一个工具链完善的最小实现），欢迎提PR

GitHub - ws456999/koa-react-ssr-starter: to understand && to explain how react ssr works

目前你可以在里面找到 react + react-router + mobx + postcss + 热更新的配置，除了react-router的配置有些差别，其他都跟client端差别不大

上面是我整理给大家的，希望今后会对大家有帮助。

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