priority-queue.js

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

    enqueue(val , priority) {
        
        let newNode = new Node(val, priority)

        this.values.push(newNode);
        this.bubbleUp();
    }

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

        while(idx > 0) {
            let parentIdx = Math.floor((idx - 1) / 2);
            let parent = this.values[ parentIdx ];

            if(element.priority >= parent.priority) break;

            // else : swapp
            this.values[ parentIdx ] = element;
            this.values[ idx ] = parent;

            idx = parentIdx;

        }

    }

    dequeue() {

        const min = this.values[ 0 ];
        const end = this.values.pop();

        if(this.values.length > 0) {
            this.values[ 0 ] = end;
            this.sinkDown();
        }

        return min;
    }

    sinkDown() {

        let idx = 0; // because sinking down will start at 0

        const length = this.values.length;
        const element = this.values[ 0 ];

        while(true) {

            let leftChildIdx = 2 * idx + 1;
            let rightChildIdx = 2 * idx + 2;

            let leftChild, rightChild;
            let swap = null; // to keep checks of swap

            // check if there is a children and its not out of bound 
            if(leftChildIdx < length) {

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

            if(rightChildIdx < length) {

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

            if(swap === null) break;

            // swapping values
            this.values[ idx ] = this.values[ swap ];
            this.values[ swap ] = element;
            idx = swap;
        }
    }
}

class Node {

    constructor(val, priority){
        this.val = val
        this.priority = priority
    }

}


let ER = new PriorityQueue();

ER.enqueue("common cold" , 3);
ER.enqueue("gunshot wound" , 0);
ER.enqueue("high fever", 2);

console.log(ER.values);

console.log(ER.dequeue())
console.log(ER.dequeue())
console.log(ER.dequeue())