added user signup feature

front/src/SignUp.vue

@@ -0,0 +1,71 @@
+<script setup>
+  import { ref, reactive, computed } from 'vue'
+  import { postBook, postSignup } from './api.js'
+  import { useRouter, useRoute } from 'vue-router'
+
+  const router = useRouter();
+
+  const user = ref({
+    username: "",
+    password: ""
+  });
+  const errors = ref(null)
+  const userError = computed(() => {
+    return extractErrorFromField("Username");
+  })
+  const passwordError = computed(() => {
+    return extractErrorFromField("Password");
+  })
+
+  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) {
+    postSignup(user)
+      .then((res) => {
+        if (res.ok) {
+          router.push('/');
+          return;
+        } else {
+          res.json().then((json) => (errors.value = json));
+        }
+      })
+  }
+</script>
+
+<template>
+  <form @submit.prevent="onSubmit">
+    <div class="field">
+      <label class="label">Username</label>
+      <div class="control">
+        <input :class="'input ' + (userError ? 'is-danger' : '')" type="text" minlength="2" maxlength="20"
+        required v-model="user.username" placeholder="Username">
+      </div>
+      <p v-if="userError" class="help is-danger">{{userError}}</p>
+    </div>
+    <div class="field">
+      <label class="label">Password</label>
+      <div class="control">
+        <input :class="'input ' + (passwordError ? 'is-danger' : '')" type="password" minlength="6"
+        maxlength="100" v-model="user.password" required placeholder="Password">
+      </div>
+      <p v-if="passwordError" class="help is-danger">{{passwordError}}</p>
+    </div>
+    <div class="field">
+      <div class="control">
+        <button class="button is-link">Submit</button>
+      </div>
+    </div>
+  </form>
+</template>
+
+<style scoped></style>