Registration of a block

Blocks in WordPress are typically bundled in a plugin and registered on both the server and client-side using block.json metadata.

While it’s possible to register blocks solely on the client-side, best practices strongly advise registering them on both the server and client. This dual registration is crucial for enabling server-side features such as Dynamic Rendering, Block Supports, Block Hooks, and Style Variations. Without server-side registration, these functionalities will not operate correctly.

For instance, if you want a block to be styled via theme.json, it must be registered on the server. Otherwise, the block won’t recognize or apply any styles assigned to it in theme.json.

The following diagram details the registration process for a block.

Open Block Registration diagram image

Registering a block with PHP (server-side)

Block registration on the server usually takes place in the main plugin PHP file with the register_block_type() function called on the init hook. This function simplifies block type registration by reading metadata stored in a block.json file.

This function is designed to register block types and primarily uses two parameters in this context, although it can accommodate more variations:

  • $block_type (string): This can either be the path to the directory containing the block.json file or the complete path to the metadata file if it has a different name. This parameter tells WordPress where to find the block’s configuration.

  • $args (array): This is an optional parameter where you can specify additional arguments for the block type. By default, this is an empty array, but it can include various options, one of which is the $render_callback. This callback is used to render blocks on the front end and is an alternative to the render property in block.json.

During the development process, the block.json file is typically moved from the src (source) directory to the build directory as part of compiling your code. Therefore, when registering your block, ensure the $block_type path points to the block.json file within the build directory.

The register_block_type() function returns the registered block type (WP_Block_Type) on success or false on failure. Here is a simple example using the render_callback.

    __DIR__ . '/build',
        'render_callback' => 'render_block_core_notice',

Here is a more complete example, including the init hook.

function minimal_block_ca6eda___register_block() {
    register_block_type( __DIR__ . '/build' );
add_action( 'init', 'minimal_block_ca6eda___register_block' );

See the full block example of the code above

Registering a block with JavaScript (client-side)

When the block has already been registered on the server, you only need to register the client-side settings in JavaScipt using the registerBlockType method from the @wordpress/blocks package. You just need to make sure you use the same block name as defined in the block’s block.json file. Here’s an example:

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

registerBlockType( 'my-plugin/notice', {
    edit: Edit,
    // ...other client-side settings
} );

While it’s generally advised to register blocks on the server using PHP for the benefits outlined in the “Benefits using the metadata file” section, you can opt to register a block solely on the client-side. The registerBlockType method allows you to register a block type using metadata.

The function accepts two parameters:

  • blockNameOrMetadata (string|Object): This can either be the block type’s name as a string or an object containing the block’s metadata, which is typically loaded from the block.json file.
  • settings (Object): This is an object containing the block’s client-side settings.
You can import the contents of the block.json file (or any other .json file) directly into your JavaScript files if you’re using a build process, such as the one provided by wp-scripts.

The settings object passed as the second parameter includes many properties, but these are the two most important ones:

  • edit: The React component that gets used in the Editor for our block.
  • save: The function that returns the static HTML markup that gets saved to the database.

The registerBlockType() function returns the registered block type (WPBlock) on success or undefined on failure. Here’s an example:

import { registerBlockType } from '@wordpress/blocks';
import { useBlockProps } from '@wordpress/block-editor';
import metadata from './block.json';

const Edit = () => <p { ...useBlockProps() }>Hello World - Block Editor</p>;
const save = () => <p { }>Hello World - Frontend</p>;

registerBlockType(, {
    edit: Edit,
} );

See the full block example of the code above

Additional resources