1-3 setTimeout 倒數計時

1. 要使用 setTimeout()，必須在卸載時去 clearTimeout()才行

   <script>
   export default {
     setup() {
       let timer = null;
   
       onMounted(() => {
         timer = setTimeout(() => {
           router.go(-1);
         }, 3000);
       });
   
       onUnmounted(() => {
         clearTimeout(timer);
       });
     },
   };
   </script>

    

2.