priority-queue.js

class Node {
    constructor (value, priority) {
        this.value = value;
        this.priority = priority;
    }
}

class PriorityQueue {
    constructor () {
        this.values = [];
    }

    enqueue (value, priority) {
        const node = new Node(value, priority);
        this.values.push(node);
        this.bubbleUp();
    }

    bubbleUp () {
        let idx = this.values.length - 1;
        const element = this.values[idx];

        while (idx > 0) {
            const parentIdx = Math.floor((idx - 1) / 2);
            const parent = this.values[parentIdx];
            if (parent.priority <= element.priority) break;
            this.values[parentIdx] = element;
            this.values[idx] = parent;
            idx = parentIdx;
        }
    }

    dequeue () {
        const max = this.values[0];
        const end = this.values.pop();
        if (this.values.length > 0){
            this.values[0] = end;
            this.sinkDown();
        }
        return max;
    }

    sinkDown () {
        let idx = 0;
        const element = this.values[idx];
        const length = this.values.length;
        while (true) {
            const leftChildIdx = 2 * idx + 1;
            const rightChildIdx = 2 * idx + 2;
            let leftChild = null;
            let rightChild = null;
            let swapIdx = null;

            if (leftChildIdx < length) {
                leftChild = this.values[leftChildIdx];
                if (leftChild.priority < element.priority) {
                    swapIdx = leftChildIdx;
                }
            }

            if (rightChildIdx < length) {
                rightChild = this.values[rightChildIdx];
                if (
                    (swapIdx === null && rightChild.priority < element.priority) ||
                    (swapIdx !== null && rightChild.priority < leftChild.priority)
                ) {
                    swapIdx = rightChildIdx;
                }
            }

            if (swapIdx === null) break;

            this.values[idx] = this.values[swapIdx];
            this.values[swapIdx] = element;
            idx = swapIdx;
        }
    }
}

const priorityQueue = new PriorityQueue();
priorityQueue.enqueue('common cold',5);
priorityQueue.enqueue('gunshot wound', 1);
priorityQueue.enqueue('high fever',4);
priorityQueue.enqueue('broken arm',2);
priorityQueue.enqueue('glass in foot',3);