YJSG comes with YjsgBrowser class which is a lightweight PHP class for detecting mobile devices browser name or browser version. You can test it by adding following code block to yjsg_custom_params.php file.

detect device or OS:

if ($detect->isMobile()) {
echo 'I am mobile device';
}
// or YJSG variable 
if ($yjsg_mobile)) {
echo 'I am mobile device';
}
// or 
if($detect->isIphone()){
echo 'Hello my name is isIphone';
}
if($detect->isIpad()){
echo 'Hello my name is isIpad';
}
if($detect->isIpod()){
echo 'Hello my name is isIpod';
}
if($detect->isBlackBerry()){
echo 'Hello my name is isBlackBerry';
}
if($detect->isiOS()){
echo 'Hello my name is isiOS';
}
if($detect->isAndroidOS()){
echo 'Hello my name is isAndroidOS';
}
if($detect->isBlackBerryOS()){
echo 'Hello my name is isBlackBerryOS';
}
if($detect->isWinOS()){
echo 'Hello my name is isWinOS';
}

detect browser version:

if($yjsgBrowser->Name == 'chrome'){
echo 'My name is ' . $yjsgBrowser->Name . ' and my version is ' . $yjsgBrowser->Version;
}
//or
if($yjsgBrowser->Name == 'msie' &&  $yjsgBrowser->Version == '8.0'){
echo 'My name is IE8. I am an old browser';
}