修复多个snackbar同时出现的问题

src/components/Main.vue

@@ -8,7 +8,6 @@ import DialogBuy from './DialogBuy.vue';
 import DialogOption from './DialogOption.vue';
 
 onMounted(() => {
-	createSnackbar('Hello World');
 	{
 		const dialog = document.getElementById("options-dialog");
 		console.log('!', dialog);

src/snackbar.js

@@ -1,9 +1,15 @@
+let lastSnackbar = null;
+
 export function createSnackbar(message) {
   const $element = document.createElement('mdui-snackbar');
   $element.setAttribute('auto-close-delay', '1000');
   $element.setAttribute('class', 'example-close-delay');
   $element.innerHTML = message;
   document.body.appendChild($element);
   $element.open = true;
+  if (lastSnackbar !== null) {
+    lastSnackbar.open = false;
+  }
+  lastSnackbar = $element;
   return $element;
 }