disable start button unless loaded

src/Player.svelte

@@ -73,7 +73,12 @@
 </script>
 
 <main>
-  <a class="link" href="javascript:;" on:click={go}>START</a>
+  <a
+    class="link"
+    class:disabled={!videoReady || !audioReady}
+    href="javascript:;"
+    on:click={go}>START</a
+  >
 
   <div id="player">
     <h2 title={videoUrl}>Video</h2>
@@ -113,4 +118,9 @@
   #audioPlayer {
     height: 128px;
   }
+
+  .disabled {
+    color: gray;
+    cursor: not-allowed;
+  }
 </style>