priority-queue.js

function PriorityQueue() {
  this.collection = [];
}

PriorityQueue.prototype = {
  enqueue([item, priority]) {
    let indexToBePlacedAt = -1;
    for (let i = 0; i < this.collection.length; i++) {
      const [, itemPriority] = this.collection[i];
      const isNewItemHigherPriority = priority < itemPriority;
      if (isNewItemHigherPriority) {
        indexToBePlacedAt = i;
      } else {
        break;
      }
    }

    if (indexToBePlacedAt > -1) {
      this.collection.splice(indexToBePlacedAt + 1, 0, [item, priority]);
    } else {
      this.collection.unshift([item, priority]);
    }
  },

  front() {
    return this.isEmpty() ? undefined : this.collection[this.size() - 1][0];
  },

  dequeue() {
    const itemToDequeue = this.collection.pop();
    return itemToDequeue ? itemToDequeue[0] : undefined;
  },

  size() {
    return this.collection.length;
  },

  isEmpty() {
    return this.size() === 0;
  }
};