Sådan implementeres rendering på serversiden i din React-app i tre enkle trin

Af Rohit Kumar

Her er hvad vi vil bygge i denne vejledning: et dejligt React-kort som dette.

I denne vejledning bruger vi gengivelse på serversiden til at levere et HTML-svar, når en bruger eller crawler rammer en side-URL. Vi håndterer sidstnævnte anmodninger på klientsiden.

Hvorfor har vi brug for det?

Lad mig guide dig til svaret.

Hvad er forskellen mellem gengivelse på klientsiden og rendering på serversiden?

I gengivelse på klientsiden downloader din browser en minimal HTML-side. Det gengiver JavaScript og udfylder indholdet i det.

Gengivelseserversiden gengiver på den anden side React-komponenterne på serveren. Outputtet er HTML-indhold.

Du kan kombinere disse to for at oprette en isomorf app.

Ulemper ved gengivelse Reager på serveren

  • SSR kan forbedre ydeevnen, hvis din applikation er lille. Men det kan også forringe ydeevnen, hvis den er tung.
  • Det øger responstiden (og det kan være værre, hvis serveren er optaget).
  • Det øger responsstørrelsen, hvilket betyder, at siden tager længere tid at indlæse.
  • Det øger applikationens kompleksitet.

Hvornår skal du bruge Server Side Rendering?

På trods af disse konsekvenser af SSR er der nogle situationer, hvor du kan og bør bruge den.

1. SEO

Hver webside ønsker at blive vist i søgninger. Ret mig, hvis jeg tager fejl.

Desværre forstår / gengiver søgemaskine-crawlere endnu ikke JavaScript.

Dette betyder, at de ser en tom side, uanset hvor nyttigt dit websted er.

Mange siger, at Googles webcrawler nu gengiver JavaScript.

For at teste dette implementerede jeg appen på Heroku. Her er hvad jeg så på Google Search Console:

En tom side.

Dette var den største grund til, at jeg udforskede rendering på serversiden. Især når det er en hjørnesteneside som f.eks. En destinationsside, blog osv.

For at kontrollere, om Google gengiver dit websted, skal du besøge:

Search Console Dashboard> Crawl> Hent som Google. Indtast sidens URL, eller lad den være tom for hjemmesiden.

Vælg FETCH AND RENDER. Når du er færdig, skal du klikke for at se resultatet.

2. Forbedre ydeevnen

I SSR afhænger applikationsydelsen af ​​serverens ressourcer og brugerens netværkshastighed. Dette gør det meget nyttigt for indholdstunge websteder.

Sig for eksempel , at du har en mellemstor mobiltelefon med lang internethastighed. Du prøver at få adgang til et websted, der downloader 4 MB data, før du kan se noget.

Ville du være i stand til at se noget på din skærm inden for 2-4 sekunder?

Vil du besøge dette websted igen?

Jeg tror ikke du ville.

En anden væsentlig forbedring er i interaktionstid for første bruger. Dette er tidsforskellen fra hvornår en bruger rammer webadressen til når de ser indhold.

Her er sammenligningen. Jeg testede det på en udviklings-Mac.

Reaktion gengivet på server

Den første interaktionstid er 300 ms. Hydrat slutter ved 400 ms. Belastningshændelsen afslutter ca. 500 ms. Du kan se dette ved at tjekke billedet ovenfor.

Reagerer gengivet på klientens browser

Den første interaktionstid er 400 ms. Belastningshændelsen afslutter ved 470ms.

Resultatet taler for sig selv. Der er 100 ms forskel i den første brugerinteraktionstid for en så lille app.

Hvordan virker det? - (4 enkle trin)

  • Opret en frisk Redux Store på hver anmodning.
  • Du kan eventuelt sende nogle handlinger.
  • Få staten ud af butikken og udfør SSR.
  • Send staten opnået i det foregående trin sammen med svaret.

We will use the state passed in the response for creating the initial state on client-side.

Before you get started, clone/download the complete example from Github and use it for reference.

Getting Started by Setting up our App

First, open your favourite editor and shell. Create a new folder for your application. Let’s start.

npm init --yes

Fill in the details. After package.json is created, copy the dependencies and scripts below into it.

Install all dependencies by running:

npm install

You need to configure Babel and webpack for our build script to work.

Babel transforms ESM and react into Node and browser-understood code.

Create a new file .babelrc and put the line below in it.

{ "presets": ["@babel/env", "@babel/react"] } 

webpack bundles our app and its dependencies into a single file. Create another file webpack.config.js with the following code in it:

const path = require('path');module.exports = { entry: { client: './src/client.js', bundle: './src/bundle.js' }, output: { path: path.resolve(__dirname, 'assets'), filename: "[name].js" }, module: { rules: [ { test: /\.js$/, exclude: /node_modules/, loader: "babel-loader" } ] } }

The build process output’s two files:

  1. assets/bundle.js — pure client side app.
  2. assets/client.js — client side companion for SSR.

The src/ folder contains the source code. The Babel compiled files go into views/. views directory will be created automatically if not present.

Why do we need to compile source files?

The reason is the syntax difference between ESM & CommonJS. While writing React and Redux, we heavily use import and export in all files.

Unfortunately, they don’t work in Node. Here comes Babel to rescue. The script below tells Babel to compile all files in the src directory and put the result in views.

"babel": "babel src -d views",

Now, Node can run them.

Copy Precoded & Static files

If you have already cloned the repository, copy from it. Otherwise download ssr-static.zip file from Dropbox. Extract it and keep these three folders inside your app directory. Here’s what they contain.

  1. React App and components resides in src/components.
  2. Redux files in src/redux/.
  3. assets/ & media/: Contain static files such as style.css and images.

Server Side

Create two new files named server.js and template.js inside the src/ folder.

1. src/server.js

Magic happens here. This is the code you’ve been searching for.

import React from 'react'; import { renderToString } from 'react-dom/server'; import { Provider } from 'react-redux'; import configureStore from './redux/configureStore'; import App from './components/app'; module.exports = function render(initialState) { // Model the initial state const store = configureStore(initialState); let content = renderToString(); const preloadedState = store.getState(); return { content, preloadedState }; };

Instead of rendering our app, we need to wrap it into a function and export it. The function accepts the initial state of the application.

Here’s how it works.

  1. Pass initialState to configureStore(). configureStore()returns a new Store instance. Hold it inside the store variable.
  2. Call renderToString() method, providing our App as input. It renders our app on the server and returns the HTML produced. Now, the variable content stores the HTML.
  3. Get the state out of Redux Store by calling getState() on store. Keep it in a variable preloadedState.
  4. Return the content and preloadedState. We will pass these to our template to get the final HTML page.

2. src/template.js

template.js exports a function. It takes title, state and content as input. It injects them into the template and returns the final HTML document.

To pass along the state, the template attaches state to window.__STATE__ inside a pt> tag.

Now you can read state on the client side by accessing window.__STATE__.

We also include the SSR companion assets/client.js client-side application in another script tag.

If you request the pure client version, it only puts assets/bundle.js inside the script tag.

The Client Side

The client side is pretty straightforward.

1. src/bundle.js

This is how you write the React and Redux Provider wrap. It is our pure client-side app. No tricks here.

import React from 'react'; import { render } from 'react-dom'; import { Provider } from 'react-redux'; import configureStore from './redux/configureStore'; import App from './components/app'; const store = configureStore(); render( , document.querySelector('#app') );

2. src/client.js

Looks familiar? Yeah, there is nothing special except window.__STATE__. All we need to do is grab the initial state from window.__STATE__ and pass it to our configureStore() function as the initial state.

Let’s take a look at our new client file:

import React from 'react'; import { hydrate } from 'react-dom'; import { Provider } from 'react-redux'; import configureStore from './redux/configureStore'; import App from './components/app'; const state = window.__STATE__; delete window.__STATE__; const store = configureStore(state); hydrate( , document.querySelector('#app') );

Let’s review the changes:

  1. Replace render() with hydrate(). hydrate() is the same as render() but is used to hydrate elements rendered by ReactDOMServer. It ensures that the content is the same on the server and the client.
  2. Read the state from the global window object window.__STATE__. Store it in a variable and delete the window.__STATE__.
  3. Create a fresh store with state as initialState.

All done here.

Putting it all together

Index.js

This is the entry point of our application. It handles requests and templating.

It also declares an initialState variable. I have modelled it with data in the assets/data.json file. We will pass it to our ssr() function.

Note: While referencing a file that is inside src/ from a file outside src/ , use normal require() and replace src/ by views/. You know the reason (Babel compile).

Routing

  1. /: By default server-rendered homepage.
  2. /client: Pure client-side rendering example.
  3. /exit: Server stop button. Only available in development.

Build & Run

It’s time to build and run our application. We can do this with a single line of code.

npm run build && npm run start

Now, the application is running at //localhost:3000.

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