add event function

addevent.js

function addEvent(target, type, handler) {
        if (target.addEventListener){
                target.addEventListener(type, handler, false);
        }else{
                target.attachEvent("on" + type,
                function(event) {
                        // Invoke the handler as a method of target,
                        // passing on the event object
                        return handler.call(target, event);
                });
        }
}