Fetch API in Vue components

Introduction

The Fetch API lets your Vue component get data from the internet easily. It helps your app show fresh information without reloading the page.

When you want to load user info from a server after the page opens.

To get a list of products from an online store API and show them.

When you need to send data to a server after a form is submitted.

To update your app with live weather data from a public API.

When you want to fetch images or content dynamically based on user actions.

Syntax

Vue

fetch(url)
  .then(response => response.json())
  .then(data => {
    // use the data here
  })
  .catch(error => {
    // handle errors here
  })

The fetch function returns a promise that resolves to a response object.

You usually call response.json() to get the data in JSON format.

Examples

Fetch data from a URL and print it in the console.

Vue

fetch('https://api.example.com/data')
  .then(res => res.json())
  .then(data => console.log(data))

Fetch with error checking and handling.

Vue

fetch('https://api.example.com/data')
  .then(res => {
    if (!res.ok) throw new Error('Network error')
    return res.json()
  })
  .then(data => console.log(data))
  .catch(err => console.error(err))

Sample Program

This Vue component fetches user data from a public API when it loads. It shows a loading message while waiting, displays the user name and email when done, and shows an error message if something goes wrong. It uses semantic HTML and ARIA roles for accessibility.

Vue

<template>
  <main>
    <h1>User Info</h1>
    <section aria-live="polite">
      <p v-if="loading">Loading user data...</p>
      <p v-if="error" role="alert" style="color: var(--error-color);">Error: {{ error }}</p>
      <article v-if="user">
        <h2>{{ user.name }}</h2>
        <p>Email: {{ user.email }}</p>
      </article>
    </section>
  </main>
</template>

<script setup>
import { ref, onMounted } from 'vue'

const user = ref(null)
const loading = ref(false)
const error = ref(null)

onMounted(async () => {
  loading.value = true
  error.value = null
  try {
    const response = await fetch('https://jsonplaceholder.typicode.com/users/1')
    if (!response.ok) throw new Error('Failed to fetch user data')
    user.value = await response.json()
  } catch (err) {
    error.value = err.message
  } finally {
    loading.value = false
  }
})
</script>

<style scoped>
:root {
  --error-color: #b00020;
}
main {
  max-width: 30rem;
  margin: 2rem auto;
  font-family: Arial, sans-serif;
  padding: 1rem;
  border: 1px solid #ccc;
  border-radius: 0.5rem;
}
article {
  background-color: #f9f9f9;
  padding: 1rem;
  border-radius: 0.25rem;
}
</style>

Important Notes

Always handle errors to avoid your app breaking if the fetch fails.

Use aria-live="polite" to announce loading or error messages to screen readers.

Keep your UI responsive by showing loading states while waiting for data.

Summary

The Fetch API helps your Vue app get data from the internet easily.

Use fetch inside lifecycle hooks like onMounted to load data when the component appears.

Show loading and error messages to keep users informed.

Practice

1. What is the main purpose of using the Fetch API inside a Vue component?

easy

A. To handle user input events like clicks

B. To style the component with CSS

C. To get data from the internet and use it in the component

D. To create new Vue components dynamically

Solution

1. Step 1: Understand Fetch API role

   The Fetch API is used to request data from a server or internet resource.

2. Step 2: Connect Fetch API to Vue component

   Inside Vue components, fetch is used to load data that the component will display or use.

3. Final Answer:

   To get data from the internet and use it in the component -> Option C

4. Quick Check:

   Fetch API = get data [OK]

Hint: Fetch API fetches data from internet for Vue components [OK]

Common Mistakes:

• Thinking Fetch API styles components
• Confusing fetch with event handling
• Using fetch to create components

2. Which is the correct way to use fetch inside a Vue 3 <script setup> component to load data on mount?

easy

A. Call fetch inside the onMounted() lifecycle hook

B. Call fetch inside a computed property

C. Use fetch directly in the template section

D. Use fetch inside a watchEffect without dependencies

Solution

1. Step 1: Identify lifecycle hook for data loading

   onMounted() runs code after the component appears, perfect for fetching data.

2. Step 2: Match fetch usage to lifecycle hook

   Calling fetch inside onMounted() ensures data loads once component is ready.

3. Final Answer:

   Call fetch inside the onMounted() lifecycle hook -> Option A

4. Quick Check:

   Fetch in onMounted = correct usage [OK]

Hint: Use onMounted() to fetch data after component loads [OK]

Common Mistakes:

• Trying to fetch data in template (not allowed)
• Using computed for async fetch (wrong usage)
• Using watchEffect without dependencies causing repeated fetch

3. What will be the output in the console when this Vue 3 <script setup> code runs?

import { ref, onMounted } from 'vue';
const data = ref(null);
const error = ref(null);
onMounted(async () => {
  try {
    const res = await fetch('https://jsonplaceholder.typicode.com/posts/1');
    data.value = await res.json();
    console.log(data.value.title);
  } catch (e) {
    error.value = 'Failed to load';
    console.log(error.value);
  }
});

medium

A. Logs undefined because data.value is never set

B. Logs 'Failed to load' always

C. Throws a syntax error because async is not allowed

D. Logs the title of the post with id 1 from the API

Solution

1. Step 1: Analyze fetch and await usage

   The code fetches a post from the API and waits for the JSON response.

2. Step 2: Check console.log output

   It logs the title property of the fetched post, so it prints the post's title.

3. Final Answer:

   Logs the title of the post with id 1 from the API -> Option D

4. Quick Check:

   Fetch success logs title [OK]

Hint: Await fetch then log data property for output [OK]

Common Mistakes:

• Assuming fetch always fails
• Thinking async is not allowed in onMounted
• Expecting undefined because of missing await

4. Identify the error in this Vue 3 <script setup> snippet that fetches data:

import { ref, onMounted } from 'vue';
const data = ref(null);
const error = ref(null);
onMounted(() => {
  fetch('https://api.example.com/data')
    .then(response => response.json())
    .then(json => data = json)
    .catch(() => error.value = 'Error fetching');
});

medium

A. Assigning json directly to data instead of data.value

B. Missing await keyword before fetch

C. Using onMounted instead of created lifecycle hook

D. Not returning the fetch promise

Solution

1. Step 1: Check how ref is updated

   Refs in Vue must be updated by setting their .value property, not the ref variable itself.

2. Step 2: Identify incorrect assignment

   The code assigns json directly to data, which breaks reactivity; it should be data.value = json.

3. Final Answer:

   Assigning json directly to data instead of data.value -> Option A

4. Quick Check:

   Update ref with .value [OK]

Hint: Update ref variables with .value, not direct assignment [OK]

Common Mistakes:

• Forgetting .value when setting ref
• Confusing async/await with then chaining
• Thinking onMounted is wrong lifecycle hook here

5. You want to fetch user data and show a loading message while waiting. Which Vue 3 <script setup> code correctly implements fetch with loading and error states?

hard

A. const loading = false;
const error = null;
const user = null;
onMounted(() => {
fetch('/user')
.then(res => res.json())
.then(data => user = data)
.catch(() => error = 'Failed');
loading = false;
});

B. const loading = ref(false);
const error = ref(null);
const user = ref(null);
onMounted(async () => {
loading.value = true;
try {
const res = await fetch('/user');
user.value = await res.json();
} catch {
error.value = 'Failed to load user';
} finally {
loading.value = false;
}
});

C. const loading = ref(true);
const error = ref('');
const user = ref({});
fetch('/user').then(res => res.json()).then(data => {
user.value = data;
loading.value = false;
}).catch(() => {
error.value = 'Error';
loading.value = false;
});

D. const loading = ref(false);
const error = ref(null);
const user = ref(null);
async function loadUser() {
loading.value = true;
const res = await fetch('/user');
user.value = await res.json();
loading.value = false;
}
onMounted(loadUser);

Solution

1. Step 1: Check reactive state setup

   const loading = ref(false); const error = ref(null); const user = ref(null); onMounted(async () => { loading.value = true; try { const res = await fetch('/user'); user.value = await res.json(); } catch { error.value = 'Failed to load user'; } finally { loading.value = false; } }); uses ref() for loading, error, and user, enabling reactivity and UI updates.

2. Step 2: Verify fetch with loading and error handling

   It sets loading true before fetch, uses try/catch for errors, and sets loading false in finally block.

3. Final Answer:

   Uses refs with onMounted, try/catch/finally for loading and error states -> Option B

4. Quick Check:

   Loading true before fetch, false after [OK]

Hint: Use ref and try/catch with finally to manage loading state [OK]

Common Mistakes:

• Not using ref for reactive state
• Setting loading false too early
• Missing error handling in async fetch