Device detection on mobile theme with Javascript

mobile-detection.js

/**
* Determine the mobile operating system.
* This function returns one of 'iOS', 'Android', 'Windows Phone', or 'unknown'.
*
* @returns {String}
*/
function getMobileOperatingSystem() {
var userAgent = navigator.userAgent || navigator.vendor || window.opera;

    // Windows Phone must come first because its UA also contains "Android"
    if (/windows phone/i.test(userAgent)) {
        return "Windows Phone";
    }

    if (/android/i.test(userAgent)) {
        return "Android";
    }

    // iOS detection from: http://stackoverflow.com/a/9039885/177710
    if (/iPad|iPhone|iPod/.test(userAgent) && !window.MSStream) {
        return "iOS";
    }

    return "unknown";
}