Simple event emmitter / observable

observable.js

function Observable() {
    this.listeners = [];
}
 
Observable.prototype = {
 
    constructor: Observable,
 
    observe: function( fn ) {
        this.listeners.push( fn );
    },
 
    unobserve: function( fn ) {
        var index;
 
        index = this.listeners.indexOf( fn );
 
        if( index > -1 ) {
            this.listeners.splice( index, 1 );
        }
 
    },
 
    update: function() {
        var listeners = this.listeners,
            len = listeners.length,
            i;
 
 
        for( i = 0; i < len; ++i ) {
            listeners[i].apply( null, arguments );
        }
 
    }
};


//Usage
 
function App() {
  this.someEventHappened = new Observable;
  this.someOtherEventHappened = new Observable;
}
 
var myApp = new App();
 
myApp.someEventHappened.observe( function() {
    console.log( "someEvent" );
});
 
myApp.someEventHappened.update(); //Should normally happen inside of the object