Composable for API calls (useFetch pattern) in Vue

Introduction

A composable for API calls helps you fetch data easily and reuse the logic in many parts of your Vue app.

When you want to get data from a server and show it in your app.

When you need to handle loading and error states while fetching data.

When you want to reuse the same data fetching logic in different components.

When you want to keep your components clean by moving API calls outside.

When you want to reactively update your UI based on the fetched data.

Syntax

Vue

import { ref } from 'vue';

export function useFetch(url) {
  const data = ref(null);
  const error = ref(null);
  const loading = ref(false);

  async function fetchData() {
    loading.value = true;
    error.value = null;
    try {
      const response = await fetch(url);
      if (!response.ok) throw new Error('Network error');
      data.value = await response.json();
    } catch (err) {
      error.value = err.message;
    } finally {
      loading.value = false;
    }
  }

  fetchData();

  return { data, error, loading, fetchData };
}

The composable returns reactive references for data, error, and loading states.

You call the fetchData function to refresh the data anytime.

Examples

Basic usage: fetch data from a URL and get reactive states.

Vue

const { data, error, loading } = useFetch('https://api.example.com/items');

You can manually reload data by calling fetchData again.

Vue

const { data, error, loading, fetchData } = useFetch('https://api.example.com/users');

// Later in code, call fetchData() to reload

You can watch the data to react when it changes.

Vue

import { watch } from 'vue';
const { data, error, loading } = useFetch('https://api.example.com/posts');

watch(data, (newData) => {
  console.log('Data changed:', newData);
});

Sample Program

This Vue component uses the useFetch composable to load posts from an API. It shows loading and error messages and lists post titles. The reload button lets users fetch the data again.

Vue

<template>
  <section aria-live="polite">
    <h2>Posts</h2>
    <button @click="fetchData" aria-label="Reload posts">Reload</button>
    <p v-if="loading">Loading posts...</p>
    <p v-if="error" role="alert">Error: {{ error }}</p>
    <ul v-if="data">
      <li v-for="post in data" :key="post.id">{{ post.title }}</li>
    </ul>
  </section>
</template>

<script setup>
import { useFetch } from './useFetch';

const { data, error, loading, fetchData } = useFetch('https://jsonplaceholder.typicode.com/posts');
</script>

Important Notes

Always handle loading and error states to improve user experience.

Use aria-live and role="alert" for accessibility when showing dynamic messages.

Composable functions keep your code clean and easy to maintain.

Summary

A composable for API calls helps fetch and manage data reactively.

It returns data, loading, and error states you can use in your components.

You can reuse the same logic across your app by importing the composable.

Practice

1. What is the main purpose of a composable like useFetch in Vue?

easy

A. To fetch data from an API and manage loading and error states reactively

B. To style components with CSS variables

C. To create Vue directives for DOM manipulation

D. To define routes in a Vue application

Solution

1. Step 1: Understand composable role

   A composable in Vue is a reusable function that encapsulates logic, often for state or side effects.

2. Step 2: Identify useFetch purpose

   The useFetch composable specifically handles API calls and manages reactive states like loading and error.

3. Final Answer:

   To fetch data from an API and manage loading and error states reactively -> Option A

4. Quick Check:

   Composable useFetch = fetch + reactive states [OK]

Hint: Composable useFetch manages API data and states reactively [OK]

Common Mistakes:

• Confusing composables with styling or routing
• Thinking composables only handle UI rendering
• Assuming composables are Vue components

2. Which of the following is the correct way to import and use a useFetch composable in a Vue component?

easy

A. const { useFetch } = Vue; const result = useFetch(url);

B. import useFetch from 'vue'; const data = useFetch(url);

C. import { useFetch } from '@/composables/useFetch'; const { data, error } = useFetch(url);

D. import { fetchData } from '@/composables'; fetchData(url);

Solution

1. Step 1: Check import syntax

   The composable is usually exported from a file and imported with curly braces if it's a named export.

2. Step 2: Using the composable

   Calling useFetch(url) returns reactive properties like data and error.

3. Final Answer:

   import { useFetch } from '@/composables/useFetch'; const { data, error } = useFetch(url); -> Option C

4. Quick Check:

   Correct import + destructure = import { useFetch } from '@/composables/useFetch'; const { data, error } = useFetch(url); [OK]

Hint: Import named composable and destructure returned refs [OK]

Common Mistakes:

• Importing from wrong path or package
• Using default import when composable is named export
• Not destructuring returned reactive properties

3. Given this useFetch composable usage:

const { data, loading, error } = useFetch('https://api.example.com/items');

What will loading.value be immediately after calling useFetch?

medium

A. null

B. true

C. false

D. undefined

Solution

1. Step 1: Understand loading state in useFetch

   Loading usually starts as true when the fetch begins to indicate data is being fetched.

2. Step 2: Check initial loading value

   Immediately after calling, loading is true until data or error updates it to false.

3. Final Answer:

   true -> Option B

4. Quick Check:

   Loading starts true during fetch [OK]

Hint: Loading is true while fetching data [OK]

Common Mistakes:

• Assuming loading starts false before fetch
• Confusing loading with data presence
• Expecting loading to be null or undefined

4. What is the main issue with this useFetch composable snippet?

export function useFetch(url) {
  const data = ref(null);
  const loading = ref(false);
  const error = ref(null);

  fetch(url)
    .then(res => res.json())
    .then(json => { data.value = json; loading.value = false; })
    .catch(err => { error.value = err; loading.value = false; });

  loading.value = true;
  return { data, loading, error };
}

medium

A. Setting loading.value = true after fetch call starts causes race condition

B. Not using async/await causes syntax error

C. data should be initialized as an empty array, not null

D. Error ref should be initialized as an empty string

Solution

1. Step 1: Analyze loading state timing

   Loading is set to false inside fetch callbacks but set to true after fetch starts, which can cause timing issues.

2. Step 2: Identify race condition

   Because loading is set to true after fetch call, it might overwrite loading false set in callbacks if fetch resolves quickly.

3. Final Answer:

   Setting loading.value = true after fetch call starts causes race condition -> Option A

4. Quick Check:

   Loading state timing error = Setting loading.value = true after fetch call starts causes race condition [OK]

Hint: Set loading true before fetch call to avoid race [OK]

Common Mistakes:

• Setting loading true after fetch call instead of before
• Confusing async/await with promises syntax errors
• Assuming initial data type must be array

5. You want to create a useFetch composable that automatically retries fetching up to 3 times if the API call fails. Which approach correctly adds this retry logic?

hard

A. Wrap fetch in a try/catch but do not retry on failure

B. Call fetch once and ignore errors, relying on component to retry

C. Use setTimeout outside the composable to call useFetch repeatedly

D. Use a recursive function inside the composable that calls fetch again on error until max retries reached

Solution

1. Step 1: Understand retry logic needs repeated fetch calls

   Retry means calling fetch again if it fails, up to a limit.

2. Step 2: Implement retry inside composable

   A recursive or loop function inside composable can retry fetch on error until max retries.

3. Step 3: Evaluate other options

   Ignoring errors or retrying outside composable breaks encapsulation; try/catch without retry misses requirement.

4. Final Answer:

   Use a recursive function inside the composable that calls fetch again on error until max retries reached -> Option D

5. Quick Check:

   Retry logic inside composable = Use a recursive function inside the composable that calls fetch again on error until max retries reached [OK]

Hint: Retry fetch inside composable with recursion or loop [OK]

Common Mistakes:

• Retrying outside composable losing reactive state control
• Ignoring errors instead of retrying
• Not limiting retry attempts causing infinite loops