@wordpress/block-editor/build-module/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;
}
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