JS Add Event

addevent.js

//from here
//https://stackoverflow.com/questions/10149963/adding-event-listener-cross-browser
//by https://stackoverflow.com/users/816620/jfriend00
//with some mods

// add event cross browser
function addEvent(elem, event, fn) {
    // avoid memory overhead of new anonymous functions for every event handler that's installed
    // by using local functions
    function listenHandler(e) {
        var ret = fn.apply(this, arguments);
        if (ret === false) {
            e.stopPropagation();
            e.preventDefault();
        }
        return(ret);
    }

    function attachHandler() {
        // set the this pointer same as addEventListener when fn is called
        // and make sure the event is passed to the fn also so that works the same too
        var ret = fn.call(elem, window.event);   
        if (ret === false) {
            window.event.returnValue = false;
            window.event.cancelBubble = true;
        }
        return(ret);
    }

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

function removeEvent(token) {
    if (token.elem.removeEventListener) {
        token.elem.removeEventListener(token.event, token.handler);
    } else {
        token.elem.detachEvent("on" + token.event, token.handler);
    }
}