heap.js

class Heap {
    constructor(comparator) {
        this.arr = [];
        this.compare = (i, j) => comparator(this.arr[i], this.arr[j]);
    }

    get size() {
        return this.arr.length;
    }

    swap(a, b) {
        const {arr} = this;
        const temp = arr[a];
        arr[a] = arr[b];
        arr[b] = temp;
    }

    add(o) {
        this.arr.push(o);
        this.bubbleDown(this.size - 1);
    }

    bubbleDown(idx) {
        if (idx === 0) {
            return;
        }

        const parent = Math.floor(idx/2);
        const res = this.compare(parent, idx);
        if (res > 0) {
            this.swap(idx, parent);
            this.bubbleDown(parent);
        }

    }

    remove() {
        const {arr} = this;
        if (!this.size) return null;
        const first = arr[0];
        this.swap(0, this.size - 1);
        this.arr.length--;
        this.bubbleUp();
        return first;
    }

    bubbleUp(idx = 0) {
        let children = [];
        if (idx === 0) {
            children.push(1);
        } else{
            children.push(idx*2, idx*2+1);
        }

        children = children.filter(i => (i < this.size && this.compare(i, idx) < 0));
        if (children.length === 2) {
            if (this.compare(children[0], children[1]) < 0) {
                this.swap(children[0], idx)
                this.bubbleUp(children[0])
            } else {
                this.swap(children[1], idx)
                this.bubbleUp(children[1])
            }
        } else if (children.length === 1) {
            if (this.compare(children[0], idx) < 0) {
                this.swap(children[0], idx);
                this.bubbleUp(children[0]);
            }
        }
    }
}

const pq = new Heap((a, b) => b - a);
pq.add(3);
pq.add(4);
pq.add(2);
pq.add(1);
console.log(pq.remove(),pq.remove(),pq.remove(),pq.remove() );