priorityQueue.js

import { createQueue } from './index';

function createPriorityQueue() {
  const lowPriorityQueue = createQueue();
  const highPriorityQueue = createQueue();

  return {
    enqueue(item, isHighPriority = false) {
      isHighPriority 
        ? highPriorityQueue.enqueue(item) 
        : lowPriorityQueue.enqueue(item)
    },
    dequeue() {
      if (!highPriorityQueue.isEmpty()) {
        return highPriorityQueue.dequeue()
      }

        return lowPriorityQueue.dequeue()
    },
    peek() {
      if (!highPriorityQueue.isEmpty()) {
        return highPriorityQueue.peek()
      }

      return lowPriorityQueue.peek()      
    },
    length() {
      return (highPriorityQueue.length + lowPriorityQueue.length)
    },
    isEmpty() {
      return (highPriorityQueue.isEmpty() && lowPriorityQueue.isEmpty())
    }
  }
}

const myQueue = createPriorityQueue()

myQueue.enqueue('A fix here')
myQueue.enqueue('A bug there')
myQueue.enqueue('A new feature')

console.log(myQueue.peek()) // A fix here

myQueue.dequeue()
console.log(myQueue.peek()) // A bug there

myQueue.enqueue('Emergency task!', true)
console.log(myQueue.peek()) // Emergency task!

myQueue.dequeue()
console.log(myQueue.peek()) // A bug there