var serviceWorkerUri = '/sw.js';

if ('serviceWorker' in navigator) {
    navigator.serviceWorker.register(serviceWorkerUri).then(function() {

        // Registration was successful. Now, check to see whether the service worker is controlling the page.
        if (navigator.serviceWorker.controller) {

            console.log('Assets cached by the controlling service worker.');

        } else {

            console.log('Please reload this page to allow the service worker to handle network operations.');

        }
    }).catch(function(error) {

        console.log('ERROR: ' + error);

    });

} else {

    // The current browser doesn't support service workers.
    console.log('Service workers are not supported in the current browser.');

}