Show how to handle the asynchronous function in the for-loop. until all the function complete, then print out "all the tasks are completed"

[Javascript] Demo asynchronous programming in for-loop .js

var demo = function (num, callback) {
  var counter = 0;
  var checkTasksComplete = function() {
    counter++;
    if (counter === num) {
      callback();
    }
  };

  // Closure: create a new function with console.log(string)
  var getFunction = function(n) {
    var string = (n % 2 === 1 ? "odd " : "even ") + n;
    return function() {
      console.log(string);

      // if all the tasks are completed, invoke the callback function
      checkTasksComplete();
    }
  };

  var getDelayTime = function(n) {
    // odd delay 50, even delay 1000
    return n % 2 === 1 ? 50 : 1000;
  };

  // start for-loop
  for (var i = 0; i < num; i++) {
    setTimeout(getFunction(i), getDelayTime(i));
  }
};

// show the odd first, then show the even
demo(200, function() {
  console.log("all the tasks are completed");
});