PWA4WP install button sample - html/css/js

functions.php

// add this code to functions.php
function enque_pwa4wp_installaction(){
    wp_enqueue_script('pwa4wp_pwa_installer',get_stylesheet_directory_uri() . '/js/pwainstall.js','','1.0',true);
}
add_action( 'wp_enqueue_scripts', 'enque_pwa4wp_installaction' );

pwa4wp_sample.css

#pwainstall {
    display: none;
}

pwa4wp_sample.html

<div id="pwainstall">
    <button id="pwainstall_button" class="square_btn">Add to Home Screen</button>
</div>

pwainstall.js

var pwa4wp_open_install = function(){
    console.log("install button show");
    jQuery('#pwainstall').css('display','block');
};
document.getElementById("pwainstall_button").addEventListener("click",function(){
    if(window.pwa4wp_installevent !== undefined ){
        window.pwa4wp_installevent.prompt();
        window.pwa4wp_installevent.userChoice.then(function(choiceResult){
            if(choiceResult === 'accepted'){
                // insert actions for installation accepted here
                console.log('pwa installation accepted.')
            }else{
                // insert actions for installation refused here
                console.log('pwa installation refused.')
            }
        });
        window.pwa4wp_installevent = null;
    }else{
        console.log("install event is undefined");
    }
});