Working with Javascript for the Block Editor

Developing blocks for the Block Editor often involves using modern JavaScript (ESNext and JSX), and most examples here in the Block Editor Handbook are written in these syntaxes.

However, this form of JavaScript must be transformed into a browser-compatible format, necessitating a build step. This process transforms, bundles, and optimizes JavaScript source code and related assets into a format suitable for production environments.

JavaScript with a build process

Using a build process for block development unlocks the full potential of modern JavaScript, facilitating the use of ESNext and JSX.

ESNext refers to Javascript’s most recent syntax and features. JSX is a syntax extension developed by the React project that enables you to write JavaScript that resembles HTML.

Since browsers cannot directly execute ESNext and JSX, these syntaxes must be transformed into browser-compatible JavaScript.

webpack is a pluggable tool that processes and bundles JavaScript for browser compatibility. Babel, a plugin for webpack, converts ESNext and JSX into standard JavaScript.

Configuring webpack and Babel can be challenging, so it’s recommended that you use the @wordpress/scripts package. This tool simplifies development by preconfiguring both, so you rarely need to write custom webpack or Babel configurations.

For an introduction, refer to the Get started with wp-scripts guide.

An overview of wp-scripts

The diagram below provides an overview of the build process when using the wp-scripts package. It’s designed to work out of the box with standard configurations for development and production environments.

Open Build Process diagram image

  • Production Mode (npm run build): In this mode, wp-scripts compiles your JavaScript, minifying the output to reduce file size and improve loading times in the browser. This is ideal for deploying your code to a live site.

  • Development Mode (npm run start): This mode is tailored for active development. It skips minification for easier debugging, generates source maps for better error tracking, and watches your source files for changes. When a change is detected, it automatically rebuilds the affected files, allowing you to see updates in real-time.

The wp-scripts package also facilitates the use of JavaScript modules, allowing code distribution across multiple files and resulting in a streamlined bundle after the build process. The block-development-example GitHub repository provides some good examples.

In most situations, no customization will be needed, but you can provide a webpack.config.js when using wp-scripts to modify the build process to suit your needs.

Javascript without a build process

Integrating JavaScript into your WordPress projects without a build process can be the most straightforward approach in specific scenarios. This is particularly true for projects that don’t leverage JSX or other advanced JavaScript features requiring compilation.

When you opt out of a build process, you interact directly with WordPress’s Javascript APIs through the global wp object. This means that all the methods and packages provided by WordPress are readily available, but with one caveat: you must manually manage script dependencies. This is done by adding the handle of each corresponding package to the dependency array of your enqueued JavaScript file.

For example, suppose you’re creating a script that registers a new block variation using the registerBlockVariation function from the blocks package. You must include wp-blocks in your script’s dependency array. This guarantees that the wp.blocks.registerBlockVariation method is available and defined by the time your script executes.

In the following example, the wp-blocks dependency is defined when enqueuing the variations.js file.

function example_enqueue_block_variations() {
        get_template_directory_uri() . '/assets/js/variations.js',
        array( 'wp-blocks' ),
        wp_get_theme()->get( 'Version' ),
add_action( 'enqueue_block_editor_assets', 'example_enqueue_block_variations' );

Then in the variations.js file, you can register a new variation for the Media & Text block like so:

        name: 'media-text-custom',
        title: 'Media & Text Custom',
        attributes: {
            align: 'wide',
            backgroundColor: 'tertiary'

For scripts that need to run in the Block Editor, make sure you use the enqueue_block_editor_assets hook coupled with the standard wp_enqueue_script function.

Refer to Enqueueing assets in the Editor for more information. You can also visit the block-development-example GitHub repository for more practical examples.

Open your browser’s dev tools and try running'core/editor').getBlocks() in the console when editing a post or when using the Site Editor. This command will return all available blocks.

Additional resources