Method dequeue

lib/PriorityQueue.js:41–48

()

  }

  dequeue() {
    for (let i = 0, sl = this._slots.length; i < sl; i += 1) {
      if (this._slots[i].length) {
        return this._slots[i].shift();
      }
    }
    return;
  }

  get head() {
    for (let i = 0, sl = this._slots.length; i < sl; i += 1) {