How to make array.forEach(asyncfn) synchronized?

Question

Say I have an array and I want to perform an async-function on each element of the array.

let a = [x1, x2, x3]

// I want to
await a.forEach(async (x) => {...         


        

Answer 1

I've been using this function for a while, in case if a dedicated library is not desired:

// usage: 

// array.asyncEach(function(item, resume) {
//   do something...
//   console.log(item); 
//   resume(); // call `resume()` to resume the cycle
// }
//
// unless resume() is called, loop doesn't proceed to the next item

Array.prototype.asyncEach = function(iterator) {
  var list    = this,
      n       = list.length,
      i       = -1,
      calls   = 0,
      looping = false;

  var iterate = function() {
    calls -= 1;
    i += 1;
    if (i === n) return;
    iterator(list[i], resume);
  };

  var loop = function() {
    if (looping) return;
    looping = true;
    while (calls > 0) iterate();
    looping = false;
  };

  var resume = function() {
    calls += 1;
    if (typeof setTimeout === 'undefined') loop();
    else setTimeout(iterate, 1);
  };
  resume();
};

Perform any async tasks inside the function, and call resume() when you are done.

I don't remember where did I get this function from.