feat: Implement ServiceWorker

feat: Implement A2H

htdocs/js/mpd.js

@@ -29,6 +29,7 @@ var current_song = new Object();
 var playstate = '';
 var settings = {};
 var alertTimeout;
+let deferredPrompt;
 
 var app = {};
 app.apps = { "Playback": { "state": "0/-/", "scrollPos": 0 },
@@ -66,6 +67,7 @@ domCache.btnNext = document.getElementById('btnNext');
 domCache.progressBar = document.getElementById('progressBar');
 domCache.volumeBar = document.getElementById('volumeBar');
 domCache.outputs = document.getElementById('outputs');
+domCache.btnAdd = document.getElementById('btnAdd');
 
 var modalConnectionError = new Modal(document.getElementById('modalConnectionError'));
 var modalSettings = new Modal(document.getElementById('modalSettings'));
@@ -456,6 +458,51 @@ function appInit() {
         }
         event.preventDefault();
     }, false);
+    
+    if ('serviceWorker' in navigator) {
+        window.addEventListener('load', function() {
+            navigator.serviceWorker.register('/sw.js', {scope: '/'}).then(function(registration) {
+                // Registration was successful
+                console.log('ServiceWorker registration successful with scope: ', registration.scope);
+            }, function(err) {
+                // registration failed :(
+                console.log('ServiceWorker registration failed: ', err);
+            });
+        });
+    }
+    
+    window.addEventListener('beforeinstallprompt', (e) => {
+        // Prevent Chrome 67 and earlier from automatically showing the prompt
+        e.preventDefault();
+        // Stash the event so it can be triggered later.
+        deferredPrompt = e;
+    });
+    
+    window.addEventListener('beforeinstallprompt', (e) => {
+        e.preventDefault();
+        deferredPrompt = e;
+        // Update UI notify the user they can add to home screen
+        domCache.btnAdd.classList.remove('hide');
+    });
+    
+    domCache.btnAdd.addEventListener('click', (e) => {
+        // hide our user interface that shows our A2HS button
+        domCache.btnAdd.classList.add('hide');
+        // Show the prompt
+        deferredPrompt.prompt();
+        // Wait for the user to respond to the prompt
+        deferredPrompt.userChoice.then((choiceResult) => {
+            if (choiceResult.outcome === 'accepted')
+                console.log('User accepted the A2HS prompt');
+            else
+                console.log('User dismissed the A2HS prompt');
+            deferredPrompt = null;
+        });
+    });
+    
+    window.addEventListener('appinstalled', (evt) => {
+        console.log('appinstalled');
+    });
 }
 
 function webSocketConnect() {