Check IE version

get-ie-version

// get internet explorer version
// returns the version (i.e 9) or false if is not IE
function getIEVersion() {
  return (/MSIE (\d+\.\d+);/.test(navigator.userAgent)) && +(/msie\s(\d+)/i.exec(navigator.userAgent)[1]);
}

// usage example
var ie = getIEVersion();
if (ie && ie < 10) {
    alert("This site is best viewed with IE10+");
}