Developer Documentation

Server-Side Rendering

Altis provides the ability to render JavaScript-based frontends on the server.

Server-side rendering allows you to provide faster load times to users, as well as a better experience for users without JavaScript or search engines.

This server-side rendering is done through v8js, a JavaScript engine integrated into PHP. v8js is installed and configured on Altis, as well as the local development environment provided by Altis.

Altis maintains the react-wp-ssr library which can be plugged into an existing React application to enable server-side rendering.


This guide will assume you're adding server-side rendering to an existing React-based theme using react-wp-scripts. Follow the Building a React app guide to set up a new theme, or consult the react-wp-ssr documentation for information about setting up react-wp-ssr with other projects.

Adding the JavaScript library

To get started, add the JS library to your application:

npm install --save react-wp-ssr

In your application, replace the ReactDOM.render call with a call to react-wp-ssr's render function:

import React from 'react';
import render from 'react-wp-ssr';

import App from './App';

render( () => <App /> );

You do not need to provide a root container ID, as this will be provided by the PHP framework.

Enabling server-side rendering

To enable server-side rendering, first add react-wp-ssr to your project's Composer packages:

composer require humanmade/react-wp-ssr

Next, call the PHP API's render function in your theme. This should replace the root container for your application. We recommend using a minimal index.php:



ReactWPSSR\render( get_stylesheet_directory() );


Your site should now render your application as before. In your browser's console, you should see a message from react-wp-ssr:

Skipping server-side render in development.

Rendering in development may cause hydration errors, as the server renders
from your built bundle, not from your development script.

Add `define( 'SSR_DEBUG_ENABLE', true )` to your wp-config to enable
in development

To test out server-side rendering, first ensure the built version of your application is up-to-date by rebuilding:

npm run build

Then add the constant to your configuration:

define( 'SSR_DEBUG_ENABLE', true );

// Optionally, set the following constant to `true` to disable loading the
// script on the client. This will render a static site on the server only,
// allowing you to verify server-side rendering is working correctly:
define( 'SSR_DEBUG_SERVER_ONLY', false );

Refresh the page and view the page's source. You should see your application rendered statically into the HTML by the server.


react-wp-ssr comes with several limitations that you should be aware of. Most well-built applications will work without any modifications, but some applications may require modifications to adapt to these limitations.

For questions about adapting your application to server-side rendering, consult the Altis team.

Using v8js Directly

v8js's PHP API can be used directly to execute JavaScript as part of your backend request.

To run JavaScript code on the server, instantiate V8Js and use the executeString method:

$v8 = new V8Js();
$result = $v8->executeString( '42 * 3.14;' );

Generally, we recommend avoiding using v8js directly, as it can be complex to configure, secure, and make performant. As v8js uses a full JavaScript engine, it can have considerably different performance characteristics. Additionally, data that is passed between PHP and JavaScript needs to be correctly sanitized and escaped for both contexts.

Ensure that any custom code is heavily tested on development and staging environments before deploying to production.