JS identifies whether the browser is android or ios

In the project, it is necessary to scan the qr code and then automatically identify whether it is android or ios system, and download for different systems.

<script type="text/javascript">

var browser = {
versions: function() {
var u = navigator.userAgent, app = navigator.appVersion;
return {//Mobile terminal browser version information
trident: u.indexOf('Trident') > -1, //IE kernel
presto: u.indexOf('Presto') > -1, //Opera kernel
webKit: u.indexOf('AppleWebKit') > -1, //Apple, Google kernel
gecko: u.indexOf('Gecko') > -1 && u.indexOf('KHTML') == -1, //Firefox kernel
mobile: !!u.match(/AppleWebKit.*Mobile.*/) || !!u.match(/AppleWebKit/), //Is it a mobile terminal
ios: !!u.match(/(i[^;]+;( U;)? CPU.+Mac OS X/), //Ios terminal
android: u.indexOf('Android') > -1 || u.indexOf('Linux') > -1, //Android terminal or uc browser
iPhone: u.indexOf('iPhone') > -1 || u.indexOf('Mac') > -1, //Whether for iPhone or QQHD browser
iPad: u.indexOf('iPad') > -1, //Whether or not the
webApp: u.indexOf('Safari') == -1 //Whether the web should be a program without a header and a bottom
};
}(),
language: (navigator.browserLanguage || navigator.language).toLowerCase()
}

if (browser.versions.ios || browser.versions.iPhone || browser.versions.iPad) {
window.location="https://itunes.apple.com/xxx";
}
else if (browser.versions.android) {
window.location="http://xxx/xxx.apk";
}

//Document.writeln (" language version: "+ browser.language);
// document.writeln(" Is it a mobile terminal: " + browser.versions.mobile);
// document.writeln(" Ios terminal: " + browser.versions.ios);
//Document.writeln (" android terminal: "+ browser.versions.android);
//Document.writeln (" iPhone: "+ browser.versions.iphone);
// document.writeln(" Whether or not the: " + browser.versions.iPad);
// document.writeln(navigator.userAgent);

</script>