Async parallel forEach and async forEach

async.js

function asyncParForEach(array, fn, callback) {
  var completed = 0;
  if (array.length === 0) {
    callback(); // done immediately
  }
  array.forEach(function(data) {
    fn(data, function() {
      completed++;
      if (completed === array.length) {
        callback();
      }
    });
  });
}


function asyncForEach(array, fn, callback) {
  array = array.slice(0);

  function processOne() {
    var item = array.pop();
    fn(item, function(result) {
      if (array.length > 0) {
        setTimeout(processOne, 0); // schedule immediately
      } else {
        callback(); // Done!
      }
    });
  }
  if (array.length > 0) {
    setTimeout(processOne, 0); // schedule immediately
  } else {
    callback(); // Done!
  }
}