function getRangesForDraftEntity(
  block: BlockNodeRecord,
  key: string,
): Array<DraftRange> {
  const ranges = [];
  block.findEntityRanges(
    c => c.getEntity() === key,
    (start, end) => {
      ranges.push({start, end});
    },
  );

  invariant(!!ranges.length, 'Entity key not found in this range.');

  return ranges;
}
Obtain the start and end positions of the range that has the
specified entity applied to it.

Entity keys are applied only to contiguous stretches of text, so this
method searches for the first instance of the entity key and returns
the subsequent range.