function addEvent(elm, evType, fn, useCapture){
    if(elm.addEventListener){
        elm.addEventListener(evType, fn, useCapture);
        return true;
    }
    else if (elm.attachEvent){
        var r = elm.attachEvent('on' + evType, fn);
        return r;
    }
    else{
        elm['on' + evType] = fn;
        return true;
    }
}