Prototype Event.StopPropagation for IE >= 8

Question

I understand the proper way to handle event.stopPropagation for IE is

if(event.stopPropagation) {
    event.stopPropagation();
} else {
    event.returnValue = false;
}

But is it possible to prototype Event so that I don't have to do the check each and everytime I use stopPropagation?

This question seemed helpful: JavaScript Event prototype in IE8 however I don't quite understand the accepted answer and how it is a prototype that can essentially be set and forget.

Answer 1

Probably this:

Event = Event || window.Event;
Event.prototype.stopPropagation = Event.prototype.stopPropagation || function() {
    this.cancelBubble = true;
}

returnValue = false is an analogue for preventDefault:

Event.prototype.preventDefault = Event.prototype.preventDefault || function () {
    this.returnValue = false;
}

Answer 2

If you're doing your own event handling in plain javascript, then you probably already have a cross browser routine for setting event handlers. You can put the abstraction in that function. Here's one that I use that mimics the jQuery functionality (if the event handler returns false, then both stopPropagation() and preventDefault() are triggered. You can obviously modify it however you want it to behave:

// refined add event cross browser
function addEvent(elem, event, fn) {
    // allow the passing of an element id string instead of the DOM elem
    if (typeof elem === "string") {
        elem = document.getElementById(elem);
    }

    function listenHandler(e) {
        var ret = fn.apply(this, arguments);
        if (ret === false) {
            e.stopPropagation();
            e.preventDefault();
        }
        return(ret);
    }

    function attachHandler() {
        // normalize the target of the event
        window.event.target = window.event.srcElement;
        // make sure the event is passed to the fn also so that works the same too
        // set the this pointer same as addEventListener when fn is called
        var ret = fn.call(elem, window.event);   
        // support an optional return false to be cancel propagation and prevent default handling
        // like jQuery does
        if (ret === false) {
            window.event.returnValue = false;
            window.event.cancelBubble = true;
        }
        return(ret);
    }

    if (elem.addEventListener) {
        elem.addEventListener(event, listenHandler, false);
    } else {
        elem.attachEvent("on" + event, attachHandler);
    }
}

Or, you can just make a utility function like this:

function stopPropagation(e) {
    if(e.stopPropagation) {
        e.stopPropagation();
    } else {
        e.returnValue = false;
    }    
}

And just call that function instead of operating on the event in each function.