ProjectDrinks

I've decided to start up the ProjectDrinks meetup again here in Montreal, if you're interested in coming down you can check out the details here.

Events in Javascript

One of the features of C# that I really enjoy is events. For the many folks out there who have never used C#, an event is an implementation of the observer pattern that allows objects to watch for certain notifications within other objects. For example in the Windows.Forms library the Button object has a Click event that you can bind an action to:

  var button = new Button();
  button.Click += (sender, ev) => {
    MessageBox.Show("Hello, world!");
  };

You can define events within your own classes and fire them easily:

  public delegate void MyEventHandler();
  public event MyEventHandler MyEvent;

  //  ... lots of code ...

  // ... in some method that triggers the event:
    if (MyEvent != null){
      MyEvent();
    }

Turns out this is fairly easily implemented in Javascript. This code here should do the trick:

function createEvent(eventName, obj){
  var event = function() {
    var ob;
    for (var i = 0; i < obj[eventName].observers.length; i++){
      ob = obj[eventName].observers[i];
      ob.apply(ob, arguments);
    }
  };

  event.observers = [];

  event.add = function(observer) {
    event.observers.push(observer);
  };

  event.remove = function(observer) {
    var i = event.observers.indexOf(observer);
    if (i >= 0){
      event.observers.splice(i, 1);
    }
  };

  obj[eventName] = event;
}

Now you can go like this:

var obj = {};

createEvent("test", obj);

obj.test.add(function(){
  alert("Hello, world!");
});

obj.test();

You can try it by clicking here.