@wordpress/block-editor/src/components/block-list/use-block-props/use-focus-first-element.js

Generic block editor.

/**
 * WordPress dependencies
 */
import { useEffect, useRef } from '@wordpress/element';
import {
	focus,
	isFormElement,
	isTextField,
	placeCaretAtHorizontalEdge,
} from '@wordpress/dom';
import { useSelect } from '@wordpress/data';

/**
 * Internal dependencies
 */
import { isInsideRootBlock } from '../../../utils/dom';
import { store as blockEditorStore } from '../../../store';

/** @typedef {import('@wordpress/element').RefObject} RefObject */

/**
 * Returns the initial position if the block needs to be focussed, `undefined`
 * otherwise. The initial position is either 0 (start) or -1 (end).
 *
 * @param {string} clientId Block client ID.
 *
 * @return {number} The initial position, either 0 (start) or -1 (end).
 */
function useInitialPosition( clientId ) {
	return useSelect(
		( select ) => {
			const {
				getSelectedBlocksInitialCaretPosition,
				__unstableGetEditorMode,
				isBlockSelected,
			} = select( blockEditorStore );

			if ( ! isBlockSelected( clientId ) ) {
				return;
			}

			if ( __unstableGetEditorMode() !== 'edit' ) {
				return;
			}

			// If there's no initial position, return 0 to focus the start.
			return getSelectedBlocksInitialCaretPosition();
		},
		[ clientId ]
	);
}

/**
 * Transitions focus to the block or inner tabbable when the block becomes
 * selected and an initial position is set.
 *
 * @param {string} clientId Block client ID.
 *
 * @return {RefObject} React ref with the block element.
 */
export function useFocusFirstElement( clientId ) {
	const ref = useRef();
	const initialPosition = useInitialPosition( clientId );
	const { isBlockSelected, isMultiSelecting } = useSelect( blockEditorStore );

	useEffect( () => {
		// Check if the block is still selected at the time this effect runs.
		if ( ! isBlockSelected( clientId ) || isMultiSelecting() ) {
			return;
		}

		if ( initialPosition === undefined || initialPosition === null ) {
			return;
		}

		if ( ! ref.current ) {
			return;
		}

		const { ownerDocument } = ref.current;

		// Do not focus the block if it already contains the active element.
		if ( isInsideRootBlock( ref.current, ownerDocument.activeElement ) ) {
			return;
		}

		// Find all tabbables within node.
		const textInputs = focus.tabbable
			.find( ref.current )
			.filter( ( node ) => isTextField( node ) );

		// If reversed (e.g. merge via backspace), use the last in the set of
		// tabbables.
		const isReverse = -1 === initialPosition;
		const target =
			textInputs[ isReverse ? textInputs.length - 1 : 0 ] || ref.current;

		if ( ! isInsideRootBlock( ref.current, target ) ) {
			ref.current.focus();
			return;
		}

		// Check to see if element is focussable before a generic caret insert.
		if ( ! ref.current.getAttribute( 'contenteditable' ) ) {
			const focusElement = focus.tabbable.findNext( ref.current );
			// Make sure focusElement is valid, contained in the same block, and a form field.
			if (
				focusElement &&
				isInsideRootBlock( ref.current, focusElement ) &&
				isFormElement( focusElement )
			) {
				focusElement.focus();
				return;
			}
		}

		placeCaretAtHorizontalEdge( target, isReverse );
	}, [ initialPosition, clientId ] );

	return ref;
}