@wordpress/block-library/build-module/table-of-contents/utils.js

Block library for the WordPress editor.

/**
 * Takes a flat list of heading parameters and nests them based on each header's
 * immediate parent's level.
 *
 * @param headingList The flat list of headings to nest.
 *
 * @return The nested list of headings.
 */
export function linearToNestedHeadingList(headingList) {
  const nestedHeadingList = [];
  headingList.forEach((heading, key) => {
    if (heading.content === '') {
      return;
    }

    // Make sure we are only working with the same level as the first iteration in our set.
    if (heading.level === headingList[0].level) {
      // Check that the next iteration will return a value.
      // If it does and the next level is greater than the current level,
      // the next iteration becomes a child of the current iteration.
      if (headingList[key + 1]?.level > heading.level) {
        // We must calculate the last index before the next iteration that
        // has the same level (siblings). We then use this index to slice
        // the array for use in recursion. This prevents duplicate nodes.
        let endOfSlice = headingList.length;
        for (let i = key + 1; i < headingList.length; i++) {
          if (headingList[i].level === heading.level) {
            endOfSlice = i;
            break;
          }
        }

        // We found a child node: Push a new node onto the return array
        // with children.
        nestedHeadingList.push({
          heading,
          children: linearToNestedHeadingList(headingList.slice(key + 1, endOfSlice))
        });
      } else {
        // No child node: Push a new node onto the return array.
        nestedHeadingList.push({
          heading,
          children: null
        });
      }
    }
  });
  return nestedHeadingList;
}
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