async.js

(function() {
  var sleep = function(ms, callback) {
    var start = new Date().getTime(), finished;

    while(!finished) {
      if ((new Date().getTime() - start) > ms){
        finished = true;
      }
    }
    if (callback)
      callback();
  };

  var randomTimeout = function() {
    return Math.ceil(Math.random() * 3000);
  };

  var noCallback = function(number) {
    sleep(randomTimeout());
    console.log("function: " + number);
  }; 

  var withCallback = function(number, callback) {
    callback(number);
  };

  var consoleLog = function(number) { 
    sleep(randomTimeout());
    console.log(number);
  };

  noCallback(1);
  noCallback(2);
  noCallback(3);
  noCallback(4);
  noCallback(5);
  noCallback(6);
  noCallback(7);
  noCallback(8);
  noCallback(9);
  noCallback(10);

  console.log('--------- With Callback ---------');
  withCallback(1, consoleLog);
  withCallback(2, consoleLog);
  withCallback(3, consoleLog);
  withCallback(4, consoleLog);
  withCallback(5, consoleLog);
  withCallback(6, consoleLog);
  withCallback(7, consoleLog);
  withCallback(8, consoleLog);
  withCallback(9, consoleLog);
  withCallback(10, consoleLog);
})();