How to check if any app is installed on the device or not?

I want to check with the help of php If I can write condition to check if any app exists on the android phone or not

Solution

I think the website is only looking if the devices is mobile. As far as I know, you can't for example make a list of the apps installed on a device. Just look if the visitor visits from a mobile device. You could implement this with the Mobile Detect class for example: http://mobiledetect.net

<?php
    // Include and instantiate the class.
    require_once 'Mobile_Detect.php';
    $detect = new Mobile_Detect;

    // Any mobile device (phones or tablets).
    if ( $detect->isMobile() ) {
        // Display WhatsApp share button
    }
?>