Javascript Design Pattern : The Observer Pattern

The Observer Pattern

var eventManager = function(){

    var subscriptions = {};
    
    function subscribe(type, fn){
        if(!subscriptions[type]) {
            subscriptions[type] = [];
        }
        if(subscriptions[type].indexOf(fn) == -1){
            subscriptions[type].push(fn);
        }
    }

    function unsubscribe(type, fn){
        var listeners = subscriptions[type];
        if(!listeners) return;

        var index = listeners.indexOf(fn);
        if(index !== -1){
            listeners.splice(index, 1);
        }
    }

    function publish(type, evntObj){
        var listeners = subscriptions[type];
        if(!listeners) return;

        if(!evntObj.type){
            evntObj.type = type;
        }

        for(var i = 0; i < listeners.length; i++){
            listeners[i](evntObj);
        }
    }

    return {
        subscribe : subscribe,
        unsubscribe : unsubscribe,
        publish : publish
    }
}


var evtMgr = eventManager()

evtMgr.subscribe('/hello', foo)
evtMgr.publish('/hello', {message : 'Hello'})

evtMgr.unsubscribe('/hello', foo)
evtMgr.publish('/hello', {message : 'Hello'}) //no output