percolateUp(pos) {
    const heap = this[kHeap];
    const compare = this[kCompare];
    const setPosition = this[kSetPosition];
    const item = heap[pos];

    while (pos > 1) {
      const parent = heap[pos / 2 | 0];
      if (compare(parent, item) <= 0)
        break;
      heap[pos] = parent;
      if (setPosition !== undefined)
        setPosition(parent, pos);
      pos = pos / 2 | 0;
    }
    heap[pos] = item;
    if (setPosition !== undefined)
      setPosition(item, pos);
  }

  removeAt(pos) {
    const heap = this[kHeap];
    const size = --this[kSize];
    heap[pos] = heap[size + 1];
    heap[size + 1] = undefined;

    if (size > 0 && pos <= size) {
      if (pos > 1 && this[kCompare](heap[pos / 2 | 0], heap[pos]) > 0)
        this.percolateUp(pos);
      else
        this.percolateDown(pos);
    }
  }

  shift() {
    const heap = this[kHeap];
    const value = heap[1];
    if (value === undefined)
      return;

    this.removeAt(1);

    return value;
  }
};