fix extract error from api call

front/src/AddBook.vue

@@ -1,6 +1,6 @@
 <script setup>
   import { ref, reactive, computed } from 'vue'
-  import { postBook } from './api.js'
+  import { postBook, extractFormErrorFromField } from './api.js'
   import { useRouter, useRoute } from 'vue-router'
 
   const router = useRouter();
@@ -11,24 +11,12 @@
   });
   const errors = ref(null)
   const titleError = computed(() => {
-    return extractErrorFromField("Title");
+    return extractFormErrorFromField("Title", errors.value);
   })
   const authorError = computed(() => {
-    return extractErrorFromField("Author");
+    return extractFormErrorFromField("Author", errors.value);
   })
 
-  function extractErrorFromField(fieldName) {
-    if (errors.value === null) {
-     return "";
-    }
-    const titleErr = errors.value.find((e) => e["field"] === fieldName);
-    if (typeof titleErr !== 'undefined') {
-      return titleErr.error
-    } else {
-      return "";
-    }
-  }
-
   function onSubmit(e) {
     postBook(book)
       .then((res) => {