//cross-browser function to add event listeners
function addEvent( obj, evType, fn ) { 
    if( obj.addEventListener ) { 
        obj.addEventListener( evType, fn, false ); 
        return true; 
    } else if( obj.attachEvent ) { 
        var r = obj.attachEvent( "on" + evType, fn ); 
        return r; 
    } else { 
        return false; 
    } 
}