Get iOS Version From http://stackoverflow.com/questions/8348139/detect-ios-version-less-than-5-with-javascript

get-ios-version.js

function iOSversion() {
  if (/iP(hone|od|ad)/.test(navigator.platform)) {
    // supports iOS 2.0 and later: <http://bit.ly/TJjs1V>
    var v = (navigator.appVersion).match(/OS (\d+)_(\d+)_?(\d+)?/);
    return [parseInt(v[1], 10), parseInt(v[2], 10), parseInt(v[3] || 0, 10)];
  }
}

ver = iOSversion();

if (ver[0] >= 5) {
  alert('This is running iOS 5 or later.');
}