JavaScript Build Setup Edit

ESNext is JavaScript written using syntax and features only available in a version newer than browser support—the support browser versions is referred to as ECMAScript 5 (ES5). JSX is a custom syntax extension to JavaScript, created by React project, that allows you to write JavaScript using a familiar HTML tag-like syntax.

See the ESNext syntax documentation for explanation and examples about common code differences between standard JavaScript and ESNext.

Let’s set up your development environment to use these syntaxes, we’ll cover development for your plugin to work with the Gutenberg project (ie: the block editor). If you want to develop on Gutenberg itself, see the Getting Started documentation.

Browsers cannot interpret or run ESNext and JSX syntaxes, so we must use a transformation step to convert these syntaxes to code that browsers can understand.

There are a few reasons to use ESNext and this extra step of transformation:

  • It makes for simpler code that is easier to read and write.
  • Using a transformation step allows for tools to optimize the code to work on the widest variety of browsers.
  • By using a build step you can organize your code into smaller modules and files that can be bundled together into a single download.

There are different tools that can perform this transformation or build step; WordPress uses webpack and Babel.

webpack is a pluggable tool that processes JavaScript and creates a compiled bundle that runs in a browser. Babel transforms JavaScript from one format to another. You use Babel as a plugin to webpack to transform both ESNext and JSX to JavaScript.

The @wordpress/scripts package abstracts these libraries away to standardize and simplify development, so you won’t need to handle the details for configuring webpack or babel. See the @wordpress/scripts package documentation for configuration details.

Quick Start

If you prefer a quick start, you can use one of the examples from the Gutenberg Examples repository and skip below. Each one of the -esnext directories in the examples repository contain the necessary files for working with ESNext and JSX.

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Both webpack and Babel are tools written in JavaScript and run using Node.js (node). Node.js is a runtime environment for JavaScript outside of a browser. Simply put, node allows you to run JavaScript code on the command-line.

First, you need to set up Node.js for your development environment. The steps required depend on your operating system, if you have a package manager installed, setup can be as straightforward as:

  • Ubuntu: apt install nodejs npm
  • macOS: brew install node
  • Windows: choco install node

If you are not using a package manager, see the developer environment setup documentation for setting up Node using nvm, or see the official Node.js download page for installers and binaries.

Note: The build tools and process occur on the command-line, so basic familiarity using a terminal application is required. Some text editors have a terminal built-in that is fine to use; Visual Studio Code and PhpStorm are two popular options.

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Node Package Manager (npm)

The Node Package Manager (npm) is a tool included with node. npm allows you to install and manage JavaScript packages. npm can also generate and process a special file called package.json, that contains information about your project and the packages your project uses.

To start a new node project, first create a directory to work in:

mkdir myguten-block
cd myguten-block

You create a new package.json running npm init in your terminal. This will walk you through creating your package.json file:

npm init

package name: (myguten-block) myguten-block
version: (1.0.0)
description: Test block
entry point: (index.js) build/index.js
test command:
git repository:
author: mkaz
license: (ISC) GPL-2.0-only
About to write to /home/mkaz/src/wp/scratch/package.json:

  "name": "myguten-block",
  "version": "1.0.0",
  "description": "Test block",
  "main": "block.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  "author": "mkaz",
  "license": "GPL-2.0-only"

Is this OK? (yes) yes

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Using npm to install packages

The next step is to install the packages required. You can install packages using the npm command npm install. If you pass the --save-dev parameter, npm will write the package as a dev dependency in the package.json file. The --save-exact parameter instructs npm to save an exact version of a dependency, not a range of valid versions. See npm install documentation for more details.

Run npm install --save-dev --save-exact @wordpress/scripts

After installing, a node_modules directory is created with the modules and their dependencies.

Also, if you look at package.json file it will include a new section:

"devDependencies": {
  "@wordpress/scripts": "6.0.0"

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Setting Up wp-scripts build

The @wordpress/scripts package handles the dependencies and default configuration for webpack and Babel. The scripts package expects the source file to compile to be found at src/index.js, and will save the compiled output to build/index.js.

With that in mind, let’s set up a basic block. Create a file at src/index.js with the following content:

import { registerBlockType } from '@wordpress/blocks';

registerBlockType( 'myguten/test-block', {
    title: 'Basic Example',
    icon: 'smiley',
    category: 'design',
    edit: () => <div>Hola, mundo!</div>,
    save: () => <div>Hola, mundo!</div>,
} );

To configure npm to run a script, you use the scripts section in package.json webpack:

  "scripts": {
    "build": "wp-scripts build"

You can then run the build using: npm run build.

After the build finishes, you will see the built file created at build/index.js. Enqueue this file in the admin screen as you would any JavaScript in WordPress, see loading JavaScript step in this tutorial, and the block will load in the editor.

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Development Mode

The build command in @wordpress/scripts runs in “production” mode. This shrinks the code down so it downloads faster, but makes it difficult to read in the process. You can use the start command which runs in development mode that does not shrink the code, and additionally continues a running process to watch the source file for more changes and rebuilds as you develop.

The start command can be added to the same scripts section of package.json:

  "scripts": {
    "start": "wp-scripts start",
    "build": "wp-scripts build"

Now, when you run npm start a watcher will run in the terminal. You can then edit away in your text editor; after each save, it will automatically build. You can then use the familiar edit/save/reload development process.

Note: keep an eye on your terminal for any errors. If you make a typo or syntax error, the build will fail and the error will be in the terminal.

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Source Control

Because a typical node_modules folder will contain thousands of files that change with every software update, you should exclude node_modules/ from your source control. If you ever start from a fresh clone, simply run npm install in the same folder your package.json is located to pull your required packages.

Likewise, you do not need to include node_modules or any of the above configuration files in your plugin because they will be bundled inside the file that webpack builds. Be sure to enqueue the build/index.js file in your plugin PHP. This is the main JavaScript file needed for your block to run.

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Dependency Management

Using wp-scripts ver 5.0.0+ build step will also produce an index.asset.php file that contains an array of dependencies and a version number for your block. For our simple example above, it is something like:
array('dependencies' => array('wp-element', 'wp-polyfill'), 'version' => 'fc93c4a9675c108725227db345898bcc');

Here is how to use this asset file to automatically set the dependency list for enqueuing the script. This prevents having to manually update the dependencies, it will be created based on the package imports used within your block.

$asset_file = include( plugin_dir_path( __FILE__ ) . 'build/index.asset.php');

    plugins_url( 'build/index.js', __FILE__ ),

See ESNext blocks in gutenberg-examples repo for full examples.

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Yes, the initial setup is a bit more involved, but the additional features and benefits are usually worth the trade off in setup time.

With a setup in place, the standard workflow is:

  1. Install dependencies: npm install
  2. Start development builds: npm start
  3. Develop. Test. Repeat.
  4. Create production build: npm run build