Heap.js

function Heap(compare = (a, b) => a - b) {
  const arr = [];
  return { push, pop, peek, size };

  function size() {
    return arr.length;
  }

  function push(v) {
    arr.push(v);
    bubble();
  }

  function pop() {
    const top = peek();
    const last = arr.pop();
    if (arr.length > 0) {
      arr[0] = last;
      sink();
    }
    return top;
  }

  function peek() {
    return arr[0];
  }

  function bubble() {
    let i = arr.length - 1;
    let p = (i - 1) >> 1;

    while (i !== 0 && compare(arr[i], arr[p]) < 0) {
      [arr[i], arr[p]] = [arr[p], arr[i]];
      i = p;
      p = (i - 1) >> 1;
    }
  }

  function sink() {
    let i = 0;
    for (;;) {
      let next = i;
      for (const childIdx of [i * 2 + 1, i * 2 + 2]) {
        if (childIdx < arr.length && compare(arr[childIdx], arr[next]) < 0) {
          next = childIdx;
        }
      }
      if (next === i) return;
      [arr[i], arr[next]] = [arr[next], arr[i]];
      i = next;
    }
  }
}