gistfile1.js

var asyncMap = function(tasks, callback){
  var results = [];
  var tasksCompleted = 0;

  var makeCallBack = function(i) {
    return function(x) {
      results[i] = x;
      tasksCompleted++;

      if (tasksCompleted === tasks.length) {
        callback(results);
      }
    }
  };

  for (var i = 0; i < tasks.length; i++) {
    tasks[i](makeCallBack(i));
  }
};