JavaScript Heap

class Heap {
  constructor(comparator = (x, y) => x > y) {
    this.data = []
    this.comparator = comparator
  }

  insert(val) {
    const data = this.data
    data.push(val)

    let index = data.length - 1
    while(index) {
      const parent = Math.floor((index - 1) / 2)
      if (!this.comparator(data[index], data[parent])) return;
      this.swap(index, parent)
      index = parent
    }
  }

  extract() {
    const data = this.data

    this.swap(0, data.length - 1)

    const val = data.pop()
    const length = data.length
    let index = 0, exchange = 2 * index + 1

    while(exchange < length) {
      const right = exchange + 1
      if (right < length && this.comparator(data[right], data[exchange])) {
        exchange = right
      }

      if (!this.comparator(data[exchange], data[index])) break

      this.swap(index, exchange)
      index = exchange
      exchange = 2 * index + 1
    }  
    return val
  }

  top() {
    return this.data.length > 0 ? this.data[0] : null
  }

  swap(i, j) {
    const data = this.data;
    [data[i], data[j]] = [data[j], data[i]]
  }
}