[upd] cleaning code

src/App.vue

 <script setup lang="ts">
-/*import { RouterLink, RouterView } from 'vue-router'*/
-import { ref, computed } from 'vue';
+import { ref, computed } from "vue";
 import { evaluate } from "mathjs";
-import HelloWorld from './components/HelloWorld.vue'
 
 const elements = ref([
   "7",
@@ -36,23 +34,19 @@ const result = computed(() => {
     return evaluate(screen_value.value);
   } catch (error) {
     console.log(error);
-    return alert("Wrong expression !!! Press clear (C) and try again.");
+    alert("ERROR : Wrong expression !!!");
+    return "Press clear (C)";
   }
 });
 
-function onClick(e: any) { 
+function onClick(e: any) {
   show_result.value = true;
 
   if (!isNaN(e) || ["/", "*", "+", "-"].includes(e)) {
     screen_value.value += e;
-  }
-
-  else if (e === "=") {
+  } else if (e === "=") {
     screen_value.value = result.value;
-
-  }
-
-  else if (e === "C") {
+  } else if (e === "C") {
     screen_value.value = "";
     show_result.value = false;
   }
@@ -65,7 +59,7 @@ function onClick(e: any) {
       <div v-if="show_result">{{ screen_value }}</div>
       <div v-else>{{ 0 }}</div>
     </div>
-  <div>
+    <div>
       <button
         v-for="e in elements"
         :key="e"

src/components/HelloWorld.vue

-<script setup lang="ts">
-defineProps<{
-  msg: string
-}>()
-</script>
-
-<template>
-  <div class="greetings">
-    <h1 class="green">{{ msg }}</h1>
-    <h3>
-      You’ve successfully created a project with
-      <a href="https://vitejs.dev/" target="_blank" rel="noopener">Vite</a> +
-      <a href="https://vuejs.org/" target="_blank" rel="noopener">Vue 3</a>. What's next?
-    </h3>
-  </div>
-</template>
-
-<style scoped>
-h1 {
-  font-weight: 500;
-  font-size: 2.6rem;
-  top: -10px;
-}
-
-h3 {
-  font-size: 1.2rem;
-}
-
-.greetings h1,
-.greetings h3 {
-  text-align: center;
-}
-
-@media (min-width: 1024px) {
-  .greetings h1,
-  .greetings h3 {
-    text-align: left;
-  }
-}
-</style>