Composable for API calls (useFetch pattern) in Vue - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a composable in Vue 3?

A composable is a reusable function that uses Vue's Composition API features like refs and reactive state to share logic across components.

beginner

What is the main purpose of the useFetch composable pattern?

The useFetch pattern helps to fetch data from APIs in a reusable way, managing loading, error, and data states inside a composable function.

intermediate

Which Vue 3 feature allows useFetch to track loading and error states reactively?

Vue 3's ref and reactive functions allow useFetch to create reactive variables for loading, error, and data states.

intermediate

How does useFetch improve code reuse compared to fetching data directly inside components?

useFetch centralizes API call logic, so multiple components can share the same fetching code without repeating it, making code cleaner and easier to maintain.

intermediate

What is a common way to handle errors inside a useFetch composable?

Inside useFetch, errors are caught in a try-catch block and stored in a reactive error variable, so components can reactively show error messages.

What does the useFetch composable typically return?

A A promise that resolves with the data

B Reactive references for data, loading, and error states

C Only the fetched data as a plain object

D A Vue component

useFetch returns reactive refs for data, loading, and error so components can reactively respond to API call states.

Which Vue Composition API function is commonly used inside useFetch to hold the loading state?

A ref

B computed

C watch

D provide

ref creates a reactive variable, perfect for tracking loading state inside useFetch.

Why should API calls be placed inside a composable like useFetch instead of directly in components?

A To avoid using Vue's reactive system

B Because components cannot make API calls

C To reuse fetching logic and keep components clean

D To make the app slower

Placing API calls in composables promotes code reuse and cleaner components.

How does useFetch handle asynchronous API calls?

A Using async/await inside the composable function

B Using setTimeout to delay calls

C Using synchronous XMLHttpRequest

D Using Vue directives

useFetch uses async/await to handle asynchronous API calls cleanly.

What should you do inside useFetch if the API call fails?

A Ignore the error silently

B Throw the error to the console only

C Reload the page automatically

D Catch the error and update a reactive error variable

Catching errors and updating a reactive error variable lets components show error messages reactively.

Explain how you would create a useFetch composable in Vue 3 to fetch data from an API and handle loading and error states.

Think about how to track states reactively and handle async calls inside a function.

Describe the benefits of using a composable like useFetch for API calls in a Vue 3 application.

Consider how sharing logic helps when multiple components need the same data.

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