Question

I write lots of little libraries and modules and usually these libraries and modules have have some events associated with them. Until now I’ve been writing these like (shortened down a lot):

Library.prototype.on = function(event, callback){
  self = this;
  self.events[event] = callback;
}

then a user would do something such as:

Library.on('foo',function(){
  console.log('bar');
});

Is there a better more performant way to do this though or is this a standard way of implementing this? I want a simple API that i can drop into any JS project to support this behavior.

Answer 1

var EventEmitter = {
    constructor: function _constructor() {
        this._events = [];
        return this;
    },
    on: function _on(ev, handler) {
        if (!this._events[ev]) {
            this._events[ev] = [];
        }
        this._events[ev].push(handler);
    },
    removeListener: function _removeListener(ev, handler) {
        if (!this._events[ev]) return;
        this._events[ev].splice(this._events[ev].indexOf(handler), 1);
    },
    removeAll: function _removeAll(ev) {
        delete this._events[ev];
    },
    emit: function _emit(ev, data) {
        if (!this._events[ev]) return;
        this._events[ev].forEach(invokeHandler);

        function invokeHandler(handler) {
            handler(data);
        }
    }
};

I have a small EventEmitter I use when I need quick and dirty custom events.

The only difference between mine and your implementation is that mine allows multiple callbacks per event.

For anything serious I use an event library like EventEmitter2