JSFiddle - React, Tailwind, and code Playground

JavaScript

var os = (function() {
    var ua = navigator.userAgent.toLowerCase();
    return {
        isWin2K: /windows nt 5.0/.test(ua),
        isXP: /windows nt 5.1/.test(ua),
        isVista: /windows nt 6.0/.test(ua),
        isWin7: /windows nt 6.1/.test(ua)
    };
}());

if(os.isWin7) {
    alert("You're using Windows 7");
}

if(os.isVista) {
    alert("You're using Windows Vista");
}

if(os.isXP) {
    alert("You're using Windows XP");
}

if(os.isWin2K) {
    alert("You're using Windows 2000");
}