var observer = {
  subscribers: {},
  on: function(type, fn){
    //check if exist, if not, define
    this.subscribers[type] = [];
    this.subscribers[type].push({fn: fn})
  },
  trigger: function(type){
    for(var i=0; i<this.subscribers[type].length; i++){
      this.subscribers[type][i].fn.call();
    }
  },
  remove: function(type, fn){
    for(var i=0; i<this.subscribers[type].length; i++){
      if(this.subscribers[type][i].fn === fn){
       this.subscribers[type].splice(i,1);
      }
    }
  }
}


var helloFn = function(){
  console.log('Hello!');
}

observer.on('sayHello', helloFn);
observer.trigger('sayHello');
observer.remove('sayHello', helloFn);
observer.trigger('sayHello');