Pre-render routes with react-snap
Not server-side rendering but still want to speed up the performance of your React site? Try pre-rendering!
react-snap is a third-party library that pre-renders pages on your site into static HTML files. This can improve First Paint times in your application.
Here's a comparison of the same application with and without pre-rendering loaded on a simulated 3G connection and mobile device:
Why is this useful? #
To solve this, many developers take the approach of rendering the application on the server instead of only booting it up on the browser. With each page/route transition, the complete HTML is generated on the server and sent to the browser, which reduces First Paint times but comes at the cost of a slower Time to First Byte.
react-snap uses Puppeteer to create pre-rendered HTML files of different routes in your application. To begin, install it as a development dependency:
npm install --save-dev react-snap
Then add a
postbuild script in your
This would automatically run the
react-snap command every time a new build of the applications made (
The last thing you will need to do is change how the application is booted. Change the
src/index.js file to the following:
import React from 'react';
import ReactDOM from 'react-dom';
import App from './App';
ReactDOM.render(<App />, document.getElementById('root'));
Instead of only using
ReactDOM.render to render the root React element directly into the DOM, this checks to see if any child nodes are already present to determine whether HTML contents were pre-rendered (or rendered on the server). If that's the case,
ReactDOM.hydrate is used instead to attach event listeners to the already created HTML instead of creating it anew.
Building the application will now generate static HTML files as payloads for each route that is crawled. You can take a look at what the HTML payload looks like by clicking the URL of the HTML request and then clicking the Previews tab within Chrome DevTools.
Flash of unstyled content #
To help prevent this, the critical CSS, or the minimum amount of CSS that is needed for the initial page to render, can be inlined directly to the
<head> of the HTML document.
react-snap uses another third-party library under the hood,
minimalcss, to extract any critical CSS for different routes. You can enable this by specifying the following in your
Taking a look at the response preview in Chrome DevTools will now show the styled page with critical CSS inlined.
If you are not server-side rendering routes in your application, use
react-snap to pre-render static HTML to your users.
- Install it as a development dependency and begin with just the default settings.
- Use the experimental
inlineCssoption to inline critical CSS if it works for your site.
- If you are using code splitting on a component level within any routes, be careful not to pre-render a loading state to your users. The
react-snapREADME covers this in more detail.