[HOW TO] Determine Device System via JS

Method 1

<script type="text/javascript">
var u = navigator.userAgent;
var isAndroid = u.indexOf('Android') > -1 || u.indexOf('Adr') > -1; //android devices
var isiOS = !!u.match(/\(i[^;]+;( U;)? CPU.+Mac OS X/); //ios devices
alert('Is Android：'+isAndroid);
alert('Is iOS：'+isiOS);
</script>

Method 2 (Full Check)

<script type="text/javascript">
// Determine deivces
var browser={
    versions:function(){
        var u = navigator.userAgent, app = navigator.appVersion;
        return {
            trident: u.indexOf('Trident') > -1, //IE Core
            presto: u.indexOf('Presto') > -1, //Opera Core
            webKit: u.indexOf('AppleWebKit') > -1, //App/Chrome Core
            gecko: u.indexOf('Gecko') > -1 && u.indexOf('KHTML') == -1,//Firefox
            mobile: !!u.match(/AppleWebKit.*Mobile.*/), //Mobile devices
            ios: !!u.match(/\(i[^;]+;( U;)? CPU.+Mac OS X/), //iOS devices
            android: u.indexOf('Android') > -1 || u.indexOf('Adr') > -1, //Android devices
            iPhone: u.indexOf('iPhone') > -1 , //Is iPhone or QQHD browser
            iPad: u.indexOf('iPad') > -1, //Is iPad
            webApp: u.indexOf('Safari') == -1, //Is web App (w/o header n footer)
            weixin: u.indexOf('MicroMessenger') > -1, //Is WeChat
            qq: u.match(/\sQQ/i) == " qq" //Is QQ
        };
    }(),
    language:(navigator.browserLanguage || navigator.language).toLowerCase()
}
</script>

To use:

//Is IE Core
if(browser.versions.trident){ alert("is IE"); }
//Is WebKit Core
if(browser.versions.webKit){ alert("is webKit"); }
//Is Mobile
if(browser.versions.mobile||browser.versions.android||browser.versions.ios){ alert("Mobile"); }

To check language:

currentLang = navigator.language;   //Determine language (except IE)
if(!currentLang){//Determine IE
    currentLang = navigator.browserLanguage;
}
alert(currentLang);

Method 3

if (/(iPhone|iPad|iPod|iOS)/i.test(navigator.userAgent)) {
    //alert(navigator.userAgent);  
    window.location.href ="iPhone.html";
} else if (/(Android)/i.test(navigator.userAgent)) {
    //alert(navigator.userAgent); 
    window.location.href ="Android.html";
} else {
    window.location.href ="pc.html";
    window.close(); // Consider to close the tab.
    setTimeout(myFunction, 3000);
};
<script>
function myFunction() {
  alert('Hello'); // Can put some code to close the tab or do sth else.
}
</script>