Generic pure js function to attach event listeners to DOM nodes

attach-function.js

var is_attachEvent = !!document.attachEvent,
    is_addEventListener = !!document.addEventListener;

function attach(target, event, fn){
    switch(true){
        case is_addEventListener:
            target.addEventListener(event, fn);
            break;
        case is_attachEvent: 
            target.attachEvent("on"+event, fn);
            break;
        default: 
            target["on" + event] = fn;
    };
}