Tutorial: building a custom block editor

This tutorial will step through the fundamentals of creating a custom instance of a “block editor” using the @wordpress/block-editor package.

Table of Contents

Introduction

The Gutenberg codebase is complex, with many packages and components, but at its core it is a tool for managing and editing blocks. Therefore, when working on the editor it is important to gain a better understanding of how block editing works at a fundamental level.

To do this, this tutorial will walk you through building a fully functioning, custom block editor “instance” within WordPress, introducing you to the key packages and components along the way.

By the end of this article, you should have gained a good understanding of how the block editor works and some of the knowledge required to put together your own block editor instances.

What we’re going to be building

We’re going to be creating an (almost) fully functioning Block Editor instance.

alt text

This block editor will not be the same Block Editor you are familiar with when creating Posts in WP Admin. Rather it will be an entirely custom instance which will live within a custom WP Admin page called (imaginatively) “Block Editor”.

Our editor will have the following features:

  • Ability to add and edit all Core Blocks.
  • Familiar visual styles and main/sidebar layout.
  • Basic block persistance between page reloads.

With that in mind, let’s start taking our first steps towards building this.

Plugin setup and organization

Our custom editor is going to be built as a WordPress Plugin. To keep things simple. we’ll call this Standalone Block Editor Demo because that is what is does. Nice!

Let’s take a look at our Plugin file structure:

alt text

Here’s a brief summary of what’s going on:

  • plugin.php – standard Plugin “entry” file with comment meta data. Requires init.php.
  • init.php – handles the initialization of the main Plugin logic. We’ll be spending a lot of time here.
  • src/ (directory) – this is where our JavaScript (and CSS) source files will live. These files are not directly enqueued by the Plugin.
  • webpack.config.js – a custom Webpack config extending the defaults provided by the @wordpress/scripts npm package to allow for custom CSS styles (via Sass).

The only item not shown above is the build/ directory, which is where our compiled JS and CSS files will be outputted by @wordpress/scripts ready to be enqueued by our Plugin.

Note: throughout this tutorial, filename references will be placed in a comment at the top of each code snippet so you can follow along.

With our basic file structure in place, we can now start looking at what package we’re going to need.

The “Core” of the Editor

Whilst the Gutenberg Editor is comprised of many moving parts, at it’s core is the @wordpress/block-editor package.

It’s role is perhaps best summarized by its own README file:

This module allows you to create and use standalone block editors.

This is great and exactly what we need! Indeed, it is the main package we’ll be using to create our custom block editor instance.

However, before we can get to working with this package in code, we’re going to need to create a home for our editor within WP Admin.

Creating the custom “Block Editor” page in WP Admin

As a first step, we need to create a custom page within WP Admin.

Note: if you’re already comfortable with the process of creating custom Admin pages in WordPress you might want to skip ahead.

Registering the Page

To do this we register our custom admin page using the standard WP add_menu_page() helper:

// init.php

add_menu_page(
    'Standalone Block Editor', // visible page name
    'Block Editor', // menu label
    'edit_posts', // required capability
    'getdavesbe', // hook/slug of page
    'getdave_sbe_render_block_editor', // function to render the page
    'dashicons-welcome-widgets-menus' // custom icon
);

Note the reference to a function getdave_sbe_render_block_editor which is the function which we will use to render the contents of the admin page.

Adding the target HTML

As the block editor is a React powered application, we now need to output some HTML into our custom page into which the JavaScript can render the block editor.

To do this we need to look at our getdave_sbe_render_block_editor function referenced in the step above.

// init.php

function getdave_sbe_render_block_editor() {
    ?>
    <div
        id="getdave-sbe-block-editor"
        class="getdave-sbe-block-editor"
    >
        Loading Editor...
    </div>
    <?php
}

Here we simply output some basic placeholder HTML.

Note that we’ve included an id attribute getdave-sbe-block-editor. Keep a note of that, a we’ll be using it shortly.

Enqueuing JavaScript and CSS

With our target HTML in place we can now enqueue some JavaScript (as well as some CSS styles) so that they will run on our custom Admin page.

To do this we hook into admin_enqueue_scripts.

First, we meed to make sure we only run our custom code on our own admin page, so at the top of our callback function let’s exit early if the page doesn’t match our page’s identifier:

// init.php

function getdave_sbe_block_editor_init( $hook ) {

    // Exit if not the correct page
    if ( 'toplevel_page_getdavesbe' !== $hook ) {
        return;
    }
}

add_action( 'admin_enqueue_scripts', 'getdave_sbe_block_editor_init' );

With this in place, we can then safely register our main JavaScript file using the standard WP wp_enqueue_script function:

// init.php

wp_enqueue_script( $script_handle, $script_url, $script_asset['dependencies'], $script_asset['version'] );

To save time and space, the assignment of the $script_ variables has been omitted. You can review these here.

Note that we register our script dependencies ($script_asset['dependencies']) as the 3rd argument – these deps are being dynamically generated using @wordpress/dependency-extraction-webpack-plugin which will ensure that WordPress provided scripts are not included in the built bundle.

We also need to register both our custom CSS styles and the WordPress default formatting library in order take advantage of some nice default styling:

// init.php

// Editor default styles
wp_enqueue_style( 'wp-format-library' );

// Custom styles
wp_enqueue_style(
    'getdave-sbe-styles', // Handle.
    plugins_url( 'build/index.css', __FILE__ ), // Block editor CSS.
    array( 'wp-edit-blocks' ), // Dependency to include the CSS after it.
    filemtime( dirname( __FILE__ ) . '/build/index.css' )
);

Inlining the editor settings

Looking at the @wordpress/block-editor package, we can see that it accepts a settings object to configure the default settings for the editor. These are available on the server side so we need to expose them for use within the JavaScript.

To do this we inline the settings object as JSON assigned to the global window.getdaveSbeSettings object:

// init.php

// Inline the Editor Settings
$settings = getdave_sbe_get_block_editor_settings();
wp_add_inline_script( $script_handle, 'window.getdaveSbeSettings = ' . wp_json_encode( $settings ) . ';' );

Registering and Rendering our custom block editor

With the PHP above in place to create our admin page, we’re now finally ready to use JavaScript to render a Block Editor into the page’s HTML.

Let’s open up our main src/index.js file.

Here we first pull in required JS packages and import our CSS styles (note using Sass requires extending the default @wordpress/scripts Webpack config).

// src/index.js

import domReady from '@wordpress/dom-ready';
import { render } from '@wordpress/element';
import { registerCoreBlocks } from '@wordpress/block-library';
import Editor from './editor';

import './styles.scss';

Next, once the DOM is ready we run a function which:

  • Grabs our editor settings from window.getdaveSbeSettings (inlined from PHP – see above).
  • Registers all the Core Gutenberg Blocks using registerCoreBlocks.
  • Renders an <Editor> component into the waiting <div> on our custom Admin page.
domReady( function() {
    const settings = window.getdaveSbeSettings || {};
    registerCoreBlocks();
    render( <Editor settings={ settings } />, document.getElementById( 'getdave-sbe-block-editor' ) );
} );

Note: it is possible to render the editor from PHP without creating an unnecessary JS global. Check out the Edit Site package in Gutenberg Core for an example of this.

Reviewing the <Editor> component

Let’s take a closer look at the <Editor> component we saw being used above.

Despite its name, this is not the actual core of the block editor. Rather it is a wrapper component we’ve created to contain the components which form the main body of our custom editor.

Dependencies

The first thing we do inside <Editor> is to pull in some dependencies.

// src/editor.js

import Notices from 'components/notices';
import Header from 'components/header';
import Sidebar from 'components/sidebar';
import BlockEditor from 'components/block-editor';

The most important of these are the internal components BlockEditor and Sidebar, which we will explore in greater detail shortly.

The remaining components are largely static elements which form the layout and surrounding UI of the editor (eg: header and notice areas).

Editor Render

With these components available we can proceed to define our <Editor> component.

// src/editor.js

function Editor( { settings } ) {
    return (
        <SlotFillProvider>
            <DropZoneProvider>
                <div className="getdavesbe-block-editor-layout">
                    <Notices />
                    <Header />
                    <Sidebar />
                    <BlockEditor settings={ settings } />
                </div>
                <Popover.Slot />
            </DropZoneProvider>
        </SlotFillProvider>
    );
}

Here we are scaffolding the core of the editor’s layout alongside a few specialised context providers which make particular functionality available throughout the component hierarchy.

Let’s examine these in more detail:

  • <SlotFillProvider> – enables the use of the “Slot/Fill” pattern through our component tree.
  • <DropZoneProvider> – enables the use of dropzones for drag and drop functionality.
  • <Notices> – custom component. Provides a “snack bar” Notice that will be rendered if any messages are dispatched to core/notices store.
  • <Header> – renders the static title “Standalone Block Editor” at the top of the editor UI.
  • <BlockEditor> – our custom block editor component. This is where things get interesting. We’ll focus a little more on this in a moment.
  • <Popover.Slot /> – renders a slot into which <Popover>s can be rendered using the Slot/Fill mechanic.

Keyboard Navigation

With this basic component structure in place the only remaining thing left to do is wrap everything in the navigateRegions HOC to provide keyboard navigation between the different “regions” in the layout.

// src/editor.js

export default navigateRegions( Editor );

The custom <BlockEditor>

Now we have a our core layouts and components in place, it’s time to explore our custom implementation of the block editor itself.

The component for this is called <BlockEditor> and this is where the magic happens.

Opening src/components/block-editor/index.js we see that this is the most complex of the components we have encountered thus far.

There’s a lot going on so let’s break this down!

Understanding the render

To start, let’s focus on what is being rendered by the <BlockEditor> component:

// src/components/block-editor/index.js

return (
    <div className="getdavesbe-block-editor">
        <BlockEditorProvider
            value={ blocks }
            onInput={ updateBlocks }
            onChange={ persistBlocks }
            settings={ settings }
        >
            <Sidebar.InspectorFill>
                <BlockInspector />
            </Sidebar.InspectorFill>
            <div className="editor-styles-wrapper">
                <BlockEditorKeyboardShortcuts />
                <WritingFlow>
                    <ObserveTyping>
                        <BlockList className="getdavesbe-block-editor__block-list" />
                    </ObserveTyping>
                </WritingFlow>
            </div>
        </BlockEditorProvider>

    </div>
);

The key components to focus on here are <BlockEditorProvider> and <BlockList>. Let’s examine these.

Understanding the <BlockEditorProvider> component

<BlockEditorProvider> is one of the most important components in the hierarchy. As we learnt earlier, it establishes a new block editing context for a new block editor.

As a result, it is fundamental to the entire goal of our project.

The children of <BlockEditorProvider> comprise the UI for the block editor. These components then have access to data (via Context) which enables them to renderand manage the Blocks and their behaviors within the editor.

// src/components/block-editor/index.js

<BlockEditorProvider
    value={ blocks } // array of block objects
    onInput={ updateBlocks } // handler to manage Block updates
    onChange={ persistBlocks } // handler to manage Block updates/persistence
    settings={ settings } // editor "settings" object
/>

BlockEditor props

We can see that <BlockEditorProvider> accepts array of (parsed) block objects as its value prop and, when there’s a change detected within the editor, calls the onChange and/or onInput handler prop (passing the new Blocks as a argument).

Internally it does this by subscribing to the provided registry (via the withRegistryProvider HOC), listening to block change events, determining whether Block changing was persistent, and then calling the appropriate onChange|Input handler accordingly.

For the purposes of our simple project these features allow us to:

  • Store the array of current blocks in state as blocks.
  • Update the blocks state in memory on onInput by calling the hook setter updateBlocks(blocks).
  • Handle basic persistence of blocks into localStorage using onChange. This is fired when block updates are considered “committed”.

It’s also worth recalling that the component accepts a settings prop. This accepts the editor settings which we inlined as JSON within init.php earlier. This configures features such as custom colors, available image sizes and much more.

Understanding the <BlockList> component

Alongside <BlockEditorProvider> the next most interesting component is <BlockList>.

This is one of the most important components as it’s role is to render a list of Blocks into the editor.

It does this in part thanks to being placed as a child of <BlockEditorProvider> which affords it full access to all information about the state of the current Blocks in the editor.

How does BlockList work?

Under the hood <BlockList> relies on several other lower-level components in order to render the list of Blocks.

The hierarchy of these components can be approximated as follows:

// Pseudo code - example purposes only

<BlockList> /* renders a list of Blocks from the rootClientId. */
    <BlockListBlock> /* renders a single "Block" from the BlockList. */
        <BlockEdit> /* renders the standard editable area of a Block. */
            <Component /> /* renders the Block UI as defined by its `edit()` implementation. */
        </BlockEdit>
    </BlockListBlock>
</BlockList>

Here’s roughly how this works together to render our list of blocks:

  • <BlockList> loops over all the Block clientIds and renders each via <BlockListBlock />.
  • <BlockListBlock /> in turn renders the individual “Block” via it’s own subcomponent <BlockEdit>.
  • Finally the Block itself is rendered using the Component placeholder component.

These are some of the most complex and involved components within the @wordpress/block-editor package. That said, if you want to have a strong grasp of how the editor works at a fundamental level, I strongly advise making a study of these components. I leave this as an exercise for the reader!

Utility components in our custom block editor

Jumping back to our own custom <BlockEditor> component, it is also worth noting the following “utility” components:

// src/components/block-editor/index.js

<div className="editor-styles-wrapper">
    <BlockEditorKeyboardShortcuts /> /* 1. */
    <WritingFlow> /* 2. */
        <ObserveTyping> /* 3. */
            <BlockList className="getdavesbe-block-editor__block-list" />
        </ObserveTyping>
    </WritingFlow>
</div>

These provide other important elements of functionality for our editor instance.

  1. <BlockEditorKeyboardShortcuts /> – enables and usage of keyboard shortcuts within the editor.
  2. <WritingFlow> – handles selection, focus management and navigation across blocks.
  3. <ObserveTyping>– used to manage the editor’s internal isTyping flag. This is used in various places, most commonly to show/hide the Block toolbar in response to typing.

Reviewing the Sidebar

Also within the render of our <BlockEditor>, is our <Sidebar> component.

// src/components/block-editor/index.js

return (
    <div className="getdavesbe-block-editor">
        <BlockEditorProvider>
            <Sidebar.InspectorFill> /* <-- SIDEBAR */
                <BlockInspector />
            </Sidebar.InspectorFill>
            <div className="editor-styles-wrapper">
                // snip
            </div>
        </BlockEditorProvider>
    </div>
);

This is used – alongside other things – to display advanced Block settings via the <BlockInspector> component.

<Sidebar.InspectorFill>
    <BlockInspector />
</Sidebar.InspectorFill>

However, the keen-eyed readers amongst you will have already noted the presence of a <Sidebar> component within our <Editor> (src/editor.js) component’s layout:

// src/editor.js
<Notices />
<Header />
<Sidebar /> // <-- eh!?
<BlockEditor settings={ settings } />

Opening src/components/sidebar/index.js we see that this is in fact the component rendered within <Editor> above. However, the implementation utilises Slot/Fill to expose a Fill (<Sidebar.InspectorFill>) which we subsequently import and render inside of our <BlockEditor> component (see above).

With this in place, we then render <BlockInspector /> as a child of the Sidebar.InspectorFill. This has the result of allowing us to keep <BlockInspector> within the React context of <BlockEditorProvider> whilst allowing it to be rendered into the DOM in a separate location (ie: in the <Sidebar>).

This might seem overly complex, but it is required in order that <BlockInspector> can have access to information about the current Block. Without Slot/Fill this setup would be extremely difficult to achieve.

Aside: <BlockInspector> itself actually renders a Slot for <InspectorControls>. This is what allows you render a <InspectorControls> component inside the edit()definition for your block and have it display within Gutenberg’s sidebar. I recommend looking into this component in more detail.

And with that we have covered the render of our custom <BlockEditor>!

Block Persistence

We’ve come a long way on our journey to create a custom block editor. But there is one major area left to touch upon – Block persistance; that is the act of having our Blocks saved and available between page refreshes.

alt text

As this is only an experiment we’ve opted to utilise the browser’s localStorage API to handle saving Block data. In a real-world scenario however you’d like choose a more reliable and robust system (eg: a database).

That said, let’s take a closer look at how we’re handling saving our Blocks.

Storing blocks in state

Opening src/components/block-editor/index.js we will notice we have created some state to store our Blocks as an array:

// src/components/block-editor/index.js

const [ blocks, updateBlocks ] = useState( [] );

As mentioned earlier, blocks is passed to the “controlled” component <BlockEditorProvider> as its value prop. This “hydrates” it with an initial set of Blocks. Similarly, the updateBlocks setter is hooked up to the onInput callback on <BlockEditorProvider> which ensures that our block state is kept in sync with changes made to blocks within the editor.

Saving Block data

If we now turn our attention to the onChange handler, we will notice it is hooked up to a function persistBlocks() which is defined as follows:

// src/components/block-editor/index.js

function persistBlocks( newBlocks ) {
    updateBlocks( newBlocks );
    window.localStorage.setItem( 'getdavesbeBlocks', serialize( newBlocks ) );
}

This function accepts an array of “committed” block changes and calls the state setter updateBlocks. In addition to this however, it also stores the blocks within LocalStorage under the key getdavesbeBlocks. In order to achieve this the Block data is serialized into Gutenberg “Block Grammar” format, meaning it can be safely stored as a string.

If we open DeveloperTools and inspect our LocalStorage we will see serialized Block data stored and updated as changes occur within the editor. Below is an example of the format:

<!-- wp:heading -->
<h2>An experiment with a standalone Block Editor in WPAdmin</h2>
<!-- /wp:heading -->

<!-- wp:paragraph -->
<p>This is an experiment to discover how easy (or otherwise) it is to create a standalone instance of the Block Editor in WPAdmin.</p>
<!-- /wp:paragraph -->

Retrieving previous block data

Having persistence in place is all well and good, but it’s useless unless that data is retrieved and restored within the editor upon each full page reload.

Accessing data is a side effect, so naturally we reach for our old (new!?) friend the useEffect hook to handle this.

// src/components/block-editor/index.js

useEffect( () => {
    const storedBlocks = window.localStorage.getItem( 'getdavesbeBlocks' );

    if ( storedBlocks && storedBlocks.length ) {
        updateBlocks( () => parse( storedBlocks ) );
        createInfoNotice( 'Blocks loaded', {
            type: 'snackbar',
            isDismissible: true,
        } );
    }
}, [] );

In this handler, we:

  • Grab the serialized block data from local storage.
  • Convert the serialized blocks back to JavaScript objects using the parse() utility.
  • Call the state setter updateBlocks causing the blocks value to be updated in state to reflect the blocks retrieved from LocalStorage.

As a result of these operations the controlled <BlockEditorProvider> component is updated with the blocks restored from LocalStorage causing the editor to show these blocks.

Finally, for good measure we generate a notice – which will display in our <Notice> component as a “snackbar” notice – to indicate that the blocks have been restored.

Wrapping up

If you’ve made it this far then congratulations! I hope you now have a better understanding of how the block editor works under the hood.

In addition, you’ve reviewed an working example of the code required to implement your own custom functioning block editor. This information should prove useful, especially as Gutenberg expands beyond editing just the Post and into Widgets, Full Site Editing and beyond!

The full code for the custom functioning block editor we’ve just built is available on Github. I encourage you to download and try it out for yourself. Experiment, then and take things even further!

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