This article explores managing WordPress metadata within the Gutenberg editor using a sidebar plugin. Gutenberg, WordPress's block editor, represents posts as a collection of blocks. While metadata can be managed using blocks, this article focuses on sidebar management for its frequent use. The tutorial assumes familiarity with ReactJS and Redux, as Gutenberg heavily utilizes these technologies.

Gutenberg's core is a React application. All editor elements—post title, content area, toolbar, and sidebar—are React components. Application state is stored in centralized JavaScript objects ("stores") managed by WordPress's data module, which shares similarities with Redux. These stores hold post data (content, title, categories) and global website information (categories, tags, posts). Modifying these stores updates the Gutenberg UI and, upon saving, the WordPress REST API updates the database.

However, Gutenberg doesn't manage metadata via these global stores by default. While legacy PHP metaboxes still function, WordPress recommends migrating them to a JavaScript approach using global stores and React components for a unified experience.

Accessing and Modifying Gutenberg's Redux-like Stores

To access these stores, open your browser's console in the Gutenberg editor and use wp.data. For example, wp.data.select('core/editor').getBlocks() retrieves the blocks in the current post. wp.data.select('core/editor').getEditedPostAttribute('title') retrieves the post title. To change data, use wp.data.dispatch(). For instance, wp.data.dispatch('core/editor').editPost({title: 'My new title'}) updates the post title. Other relevant stores include core (global website information) and core/edit-post (editor UI state).

Creating a WordPress Plugin for a Gutenberg Sidebar

To add a React sidebar component, create a WordPress plugin. This involves setting up a plugin folder (e.g., gutenberg-sidebar), creating a plugin.php file (the plugin's entry point), and using npm to manage JavaScript dependencies (@wordpress/scripts, @wordpress/edit-post, @wordpress/plugins, @wordpress/i18n, @wordpress/components, @wordpress/data). The plugin.php enqueues the JavaScript bundle created by npm run build.

Registering a Gutenberg Plugin and Sidebar

The JavaScript code (in src/index.js) uses registerPlugin from @wordpress/plugins to register a plugin. PluginSidebar and PluginSidebarMoreMenuItem from @wordpress/edit-post create the sidebar and a menu item to toggle it.

Handling Metadata in the Classic Editor

The tutorial demonstrates managing metadata in the classic editor using PHP metaboxes and functions like add_meta_box, get_post_meta, update_post_meta, and wp_verify_nonce. The __back_compat_meta_box option hides the metabox when Gutenberg is active.

Managing Metadata with JavaScript

To manage custom fields (e.g., _myprefix_text_metafield) in Gutenberg using JavaScript, register the field using register_meta with show_in_rest: true, a sanitize_callback, and an auth_callback to allow REST API updates. Use wp.data.select('core/editor').getEditedPostAttribute('meta') to retrieve and wp.data.dispatch('core/editor').editPost({meta: {_myprefix_text_metafield: 'new value'}}) to update metadata.

Creating a React Component

A React component (PluginMetaFields) is created using PanelBody and TextControl from @wordpress/components. withSelect and withDispatch from @wordpress/data connect the component to the Redux-like store, enabling data retrieval and updates. The onChange event dispatches updates to the store. Finally, a ColorPicker component is added to demonstrate using other components from @wordpress/components. The complete code is available on GitHub.

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