javascript if screen width

if ($(window).width() < 960) {
   alert('Less than 960');
}
else {
   alert('More than 960');
}

var win = window,
    doc = document,
    docElem = doc.documentElement,
    body = doc.getElementsByTagName('body')[0],
    x = win.innerWidth || docElem.clientWidth || body.clientWidth,
    y = win.innerHeight|| docElem.clientHeight|| body.clientHeight;
alert(x + ' × ' + y);