javascript - addEventListener on custom object

Question

I've created an object that has several methods. Some of these methods are asynchronous and thus I want to use events to be able to perform actions when the methods are done. To do this I tried to add the addEventListener to the object.

jsfiddle

var iSubmit = {
    addEventListener: document.addEventListener || document.attachEvent,
    dispatchEvent: document.dispatchEvent,
    fireEvent: document.fireEvent,   


    //the method below is added for completeness, but is not causing the problem.

    test: function(memo) {
        var name = "test";
        var event;
        if (document.createEvent) {
            event = document.createEvent("HTMLEvents");
            event.initEvent(name, true, true);
        } else {
            event = document.createEventObject();
            event.eventType = name;
        }
        event.eventName = name;
        event.memo = memo || { };

        if (document.createEvent) {
            try {
                document.dispatchEvent(event);
            } catch (ex) {
                iAlert.debug(ex, 'iPushError');
            }
        } else {
            document.fireEvent("on" + event.eventType, event);
        }
    }
}

iSubmit.addEventListener("test", function(e) { console.log(e); }, false);


//This call is added to have a complete test. The errors are already triggered with the line before this one.

iSubmit.test();

This will return an error: Failed to add eventlisterens: TypeError: 'addEventListener' called on an object that does not implement interface EventTarget."

Now this code will be used in a phonegap app and when I do, it is working on android/ios. During testing, however, it would be nice if I could get it to work in at least a single browser.

PS> I know I could enable bubbling and then listen to the document root, but I would like to have just a little bit OOP where each object can work on its own.

Answer 1

addEventListener is intended for DOM Elements that implements certain event-related interfaces. If you want an event system on pure JavaScript objects, you are looking for a custom event system. An example would be Backbone.Events in Backbone.js. The basic idea is using an object as a hash to keep track of registered callbacks.

Personally I use this: emitter.

It's a fairly simple and elegant solution - with sweet short method names like on(), off() and emit(). you can either create new instances with new Emitter(), or use Emitter(obj) to mix event capabilities into existing objects. Note this library is written for use with a CommonJS module system, but you can use it anywhere else by removing the module.exports = ... line.