asyncMapPool.js

Array.prototype.asyncMapPool = async function(n, t) {
  var r = [],
    i = this.map(() => !1),
    o = this.length,
    e = this;
  return new Promise(function(a, s) {
    function f() {
      if (h < o) {
        var t = h;
        r.push(
          n(e[h], h, e).then(function(n) {
            return (
              (i[t] = !0),
              0 === i.filter(n => !1 === n).length && a(Promise.all(r)),
              f(),
              n
            );
          })
        );
      }
      h++;
    }
    for (var h = 0; h < t; ) f();
  });
};

function getSquareAsync(v, i, arr) {
  return new Promise(resolve =>
    setTimeout(() => {
      console.log(`executing getSquareAsync at ${getTime()}, ${v}, ${i}`);
      resolve(v * v);
    }, 2000)
  );
}

async function run() {
  var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
  
  var result2 = await arr.asyncMapPool(getSquareAsync, 3);
  console.log(`result2 @ ${getTime()}`, result2);
}

run();

result.txt

executing getSquareAsync at 2.021, 1, 0
executing getSquareAsync at 2.022, 2, 1
executing getSquareAsync at 2.022, 3, 2
executing getSquareAsync at 4.025, 4, 3
executing getSquareAsync at 4.025, 5, 4
executing getSquareAsync at 4.025, 6, 5
executing getSquareAsync at 6.026, 7, 6
executing getSquareAsync at 6.026, 8, 7
executing getSquareAsync at 6.026, 9, 8
executing getSquareAsync at 8.028, 10, 9
result2 @ 8.029 [ 1, 4, 9, 16, 25, 36, 49, 64, 81, 100 ]