Why are callbacks more “tightly coupled” than promises?(stackoverflow.com)

    var getData = function(callback){
        showLoadingScreen();
        $.ajax("http://someurl.com", {
            complete: function(data){
                hideLoadingScreen();
                callback(data);
            }
        });		
    };

    var loadData = function(){
        getData(doSomethingWithTheData);
    }

    var doSomethingWithTheData = function(data){
        //do something with data
    };

  type Promise a = (a -> IO ()) -> IO ()
  getData :: Promise String

  getData :: (String -> IO ()) -> IO ()

  instance Monad Promise where 
    return x = \k -> k x
    fmap f p = \k -> p (k . f)
    mx >>= fxmy = \k -> mx (\x -> fxmy x k)

  //model
  User.get = function() {
    return getData();
  };
  User.getOdd = function() {
    return User.get().then(filterOdd);
  };
  
  //controller
  someControllerAction = function() {
    User.getOdd().then(redirectToHomepageIfEmpty);
  };

  //model
  User.get = function(callback) {
    getData(callback)
  }
  User.getOdd = function(callback) {
    User.get(function(data) {
      if (typeof callback == "function") {
        callback(filterOdd(data));
      }
    });
  };

  //controller
  someControllerAction = function() {
    User.getOdd(redirectToHomepageIfEmpty)
  };

  jQuery.when(User.getOdd(), Pinterest.search("something")).then(doSomething)

    void loadData = function(){
      showLoadingScreen();
      $.ajax("http://someurl.com", {
        complete: hideLoadingScreen(function(data){
          //do something with the data
        })
      });
    };

    function hideLoadingScreen(f) {
        return function(e) {
            f(e);
            doHide();
        };
    }

    // You may call this syntactic sugar
    var p1 = new Promise(function(response, reject) {
        setTimeout(function(){ 
            response(Math.random() * 1000); 
        });
    }).then(function(val){ console.log(val); return val; });
    
    // But here's the magical decoupled call
    p1.then(function(val) { console.log(val); });