Data Structure Max Heap.js

'use strict'

class MaxHeap {
  constructor() {
    this.arr = [];
  }

  peek() {
    return this.arr[0] || null;
  }

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

  pollMax() {
    var arr = this.arr;
    var len = arr.length;

    if(len === 0) {
      return null;
    }

    var max = arr[0];
    arr[0] = arr[len - 1] // replace max value with the last value

    arr.pop();

    this.sinkDown(0);

    return max;
  }

  add(val) {
    var arr = this.arr;
    arr.push(val);
    this.bubbleUp(arr.length - 1);
  }

  bubbleUp(n) {
    var arr = this.arr;

    while(n > 0) {
      // [3,2,1] 3 as root, 2 as left child and 1 as right child 
      // 2 has idx = 1 and 1 has idx = 2 
      // 1/2 will result in parent idx = 0 
      // and 2/2 will result in parent idx = 1. So we need to add one to them and -1 at the end
      var parentN = Math.floor((n + 1)/2) - 1;

      if(arr[parentN] > arr[n]) {
        break;
      }

      var tmp = arr[n];
      arr[n] = arr[parentN];
      arr[parentN] = tmp;
      n = parentN;
    } 
  }

  sinkDown(n) {
    var arr = this.arr;
    var len = arr.length;
    var val = arr[n];
  
    while(true) {
      
      var swap = null;
      var child2N = n*2 + 2; // root = 0 right child idx is (0 + 1)*2 = 2
      var child1N = n*2 + 1; // right child idx - 1 = 1 for root's left child
      
      if(child1N < len && arr[child1N] > val) {
        swap = child1N;
      }

      if(child2N < len && arr[child2N] > val && arr[child2N] >= arr[child1N]) {
        swap = child2N;
      }
    
      if(swap === null) {
        break;
      }

      var tmp = arr[n];
      arr[n] = arr[swap];
      arr[swap] = tmp;
      n = swap;
    } 
  }
}

var m = new MaxHeap();
m.add(4);
m.add(1);
m.add(2);
m.add(1);
m.add(15);
m.add(3);
m.add(4);
m.add(3);
m.add(3);

m.add(3);
m.add(4);
m.add(-1);

m.add(-1);
m.add(1);
m.add(10);

m.add(-1);
m.add(4);
m.add(8);
m.add(9);
m.add(100);
m.add(3);
m.add(7);
m.add(9);
m.add(4);

console.log(m.arr);
console.log(m.pollMax());
console.log(m.pollMax());
console.log(m.pollMax());
console.log(m.pollMax());
console.log(m.pollMax());
console.log(m.pollMax());
console.log(m.pollMax());
console.log(m.pollMax());
console.log(m.pollMax());
console.log(m.pollMax());
console.log(m.pollMax());
console.log(m.pollMax());
console.log(m.pollMax());
console.log(m.pollMax());
console.log(m.pollMax());
console.log(m.pollMax());
console.log(m.pollMax());
console.log(m.pollMax());
console.log(m.pollMax());
console.log(m.pollMax());
console.log(m.pollMax());
console.log(m.pollMax());
console.log(m.pollMax());
console.log(m.pollMax());
console.log(m.pollMax());
console.log(m.pollMax());
console.log(m.pollMax());