How to use the lib0/iterator.js.iteratorMap function in lib0

keys () {
    return iterator.iteratorMap(createMapIterator(this._map), /** @param {any} v */ v => v[0])
  }

entries () {
    return iterator.iteratorMap(createMapIterator(this._map), /** @param {any} v */ v => [v[0], v[1].content.getContent()[v[1].length - 1]])
  }

values () {
    return iterator.iteratorMap(createMapIterator(this._map), /** @param {any} v */ v => v[1].content.getContent()[v[1].length - 1])
  }