silverstripe-progressivewebapp/resources/js/progressivewebapp.js

if ('serviceWorker' in navigator) {
    var baseHref = (document.getElementsByTagName('base')[0] || {}).href;
    if(baseHref){
        navigator.serviceWorker.register(baseHref + 'service-worker.js').then(function() {
            //console.log('Service Worker Registered');
        });
    }
}