Kako u tri jednostavna koraka implementirati prikazivanje na strani poslužitelja u svojoj aplikaciji React

Napisao Rohit Kumar

Evo što ćemo izgraditi u ovom vodiču: lijepa React kartica poput ove.

U ovom uputstvu koristit ćemo prikazivanje na strani poslužitelja za isporuku HTML odgovora kada korisnik ili alat za indeksiranje pogodi URL stranice. Potonje ćemo zahtjeve rješavati na strani klijenta.

Zašto nam to treba?

Dopustite mi da vas vodim do odgovora.

Koja je razlika između prikazivanja na strani klijenta i prikazivanja na strani poslužitelja?

U klijentskom prikazivanju vaš preglednik preuzima minimalnu HTML stranicu. Prikazuje JavaScript i ispunjava sadržaj.

Renderiranje na strani poslužitelja, s druge strane, generira React komponente na poslužitelju. Rezultat je HTML sadržaj.

Možete kombinirati ovo dvoje kako biste stvorili izomorfnu aplikaciju.

Protiv prikazivanja reakcije na poslužitelju

  • SSR može poboljšati izvedbu ako je vaša aplikacija mala. Ali također može pogoršati performanse ako je velika.
  • Povećava vrijeme odziva (a može biti i gore ako je poslužitelj zauzet).
  • Povećava veličinu odgovora, što znači da se stranici treba više vremena za učitavanje.
  • Povećava složenost primjene.

Kada biste trebali koristiti prikazivanje na bočnoj strani poslužitelja?

Unatoč tim posljedicama SSR-a, postoje neke situacije u kojima ga možete i trebate koristiti.

1. SEO

Svaka web stranica želi se pojaviti u pretraživanjima. Ispravi me ako griješim.

Nažalost, alati za indeksiranje tražilice još ne razumiju / generiraju JavaScript.

To znači da vide praznu stranicu, bez obzira na to koliko je korisna vaša web lokacija.

Mnogi ljudi kažu da Googleov alat za indeksiranje sada prikazuje JavaScript.

Da bih to testirao, rasporedio sam aplikaciju na Heroku. Evo što sam vidio na Google Search Consoleu:

Prazna stranica.

To je bio najveći razlog zašto sam istražio prikazivanje na strani poslužitelja. Pogotovo kada se radi o stranici temelja kao što je odredišna stranica, blog itd.

Da biste provjerili prikazuje li Google vašu web lokaciju, posjetite:

Nadzorna ploča Search Console> indeksiranje> Dohvati kao Google. Unesite URL stranice ili ostavite prazno za početnu stranicu.

Odaberite DOBITI I IZVODITI. Kada završite, kliknite da biste vidjeli rezultat.

2. Poboljšati izvedbu

U SSR-u izvedba aplikacije ovisi o resursima poslužitelja i brzini mreže korisnika. To ga čini vrlo korisnim za web lokacije s velikim sadržajem.

Na primjer , recite da imate mobitel srednje cijene s sporom brzinom interneta. Pokušavate pristupiti web mjestu koje preuzima 4 MB podataka prije nego što možete išta vidjeti.

Biste li mogli vidjeti nešto na svom zaslonu u roku od 2–4 sekunde?

Biste li ponovno posjetili to mjesto?

Mislim da ne biste.

Još jedno veliko poboljšanje je vrijeme interakcije prvog korisnika. To je razlika u vremenu od trenutka kada korisnik pogodi URL do trenutka kada vidi sadržaj.

Evo usporedbe. Testirao sam ga na razvojnom Macu.

Reagirajte prikazano na poslužitelju

Prvo vrijeme interakcije je 300 ms. Hidrat završava na 400ms. Događaj opterećenja izlazi na otprilike 500 ms. To možete vidjeti provjerom gornje slike.

Reagirajte prikazano na klijentovom pregledniku

Prvo vrijeme interakcije je 400ms. Događaj opterećenja izlazi na 470ms.

Rezultat govori sam za sebe. Razlika od 100 ms u vremenu interakcije prvog korisnika za tako malu aplikaciju.

Kako radi? - (4 jednostavna koraka)

  • Stvorite svježu Redux trgovinu na svaki zahtjev.
  • Po želji uputite neke radnje.
  • Izvucite državu iz trgovine i izvršite SSR.
  • Pošaljite stanje dobiveno u prethodnom koraku zajedno s odgovorom.

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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