Nuxt data fetching (useFetch, useAsyncData) in Vue - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Nuxt component using useFetch?

Consider this Nuxt 3 component that fetches user data:

const { data, pending, error } = useFetch('/api/user')

return () => {
  if (pending.value) return 'Loading...'
  if (error.value) return 'Error!'
  return `User: ${data.value.name}`
}

Assuming the API returns { name: 'Alice' }, what will the rendered output be?

Vue

const { data, pending, error } = useFetch('/api/user')

return () => {
  if (pending.value) return 'Loading...'
  if (error.value) return 'Error!'
  return `User: ${data.value.name}`
}

A User: Alice

B Loading...

C User: undefined

D Error!

💡 Hint

Think about what useFetch returns and when the component renders.

useFetch returns reactive references. Once the data is fetched successfully, pending becomes false and data.value holds the API response. So the component renders User: Alice.

❓ state_output

intermediate

What is the value of data after useAsyncData resolves?

Given this Nuxt 3 setup:

const { data, error } = await useAsyncData('post', () => $fetch('/api/post/1'))

If the API returns { id: 1, title: 'Hello' }, what is data.value?

Vue

const { data, error } = await useAsyncData('post', () => $fetch('/api/post/1'))

A null

B undefined

C { id: 1, title: 'Hello' }

D Error object

💡 Hint

useAsyncData resolves with the fetched data inside data.value.

After awaiting useAsyncData, data.value contains the API response object.

📝 Syntax

advanced

Which option correctly uses useFetch with error handling in Nuxt 3?

Choose the code snippet that correctly fetches data and handles errors using useFetch in a Nuxt 3 setup.

A

const { data, error } = useFetch('/api/data')
if (error.value) console.error(error.value)

B

const { data, error } = useFetch('/api/data')
if (error) console.error(error)

C

const { data, error } = await useFetch('/api/data')
if (error.value) console.error(error.value)

D

const { data, error } = useFetch('/api/data')
if (error.value) console.log(data.value)

💡 Hint

Remember that error is a ref and must be accessed with .value.

useFetch returns refs for data and error. To check error, use error.value. Option A correctly checks and logs the error.

🔧 Debug

advanced

Why does this useAsyncData call cause a runtime error?

Examine this code snippet:

const { data } = useAsyncData(() => fetch('/api/items').then(res => res.json()))
console.log(data.value.length)

What causes the runtime error?

Vue

const { data } = useAsyncData(() => fetch('/api/items').then(res => res.json()))
console.log(data.value.length)

A The <code>then</code> callback returns a promise instead of data

B <code>data.value</code> is undefined because <code>useAsyncData</code> is asynchronous and data is not ready yet

C The fetch URL is incorrect causing a network error

D The <code>console.log</code> is inside the async callback causing a syntax error

💡 Hint

Think about when data.value is available after calling useAsyncData.

useAsyncData returns a ref that is initially undefined until the promise resolves. Accessing data.value.length immediately causes an error because data.value is undefined at that moment.

🧠 Conceptual

expert

Which statement about useFetch vs useAsyncData in Nuxt 3 is correct?

Choose the correct statement about the differences between useFetch and useAsyncData in Nuxt 3.

A <code>useAsyncData</code> returns raw promises, <code>useFetch</code> returns refs

B <code>useFetch</code> automatically serializes and deserializes JSON, while <code>useAsyncData</code> requires manual parsing

C <code>useFetch</code> can only be used on client side, <code>useAsyncData</code> only on server side

D <code>useAsyncData</code> caches data by key and supports server-side rendering, <code>useFetch</code> does not cache by default

💡 Hint

Think about caching and SSR support differences.

useAsyncData caches data by a key and is designed for SSR and hydration. useFetch is a simpler wrapper around fetch with reactive refs but does not cache by default.

Practice

1. What is the main difference between useFetch and useAsyncData in Nuxt?

easy

A. useAsyncData automatically refreshes data, useFetch never does.

B. useAsyncData requires a unique key for caching, useFetch does not.

C. useFetch is only for server-side, useAsyncData is client-side only.

D. useFetch caches data with a key, useAsyncData fetches without caching.

Solution

1. Step 1: Understand useFetch behavior

   useFetch fetches data from a URL quickly but does not require a key for caching.

2. Step 2: Understand useAsyncData behavior

   useAsyncData needs a unique key to cache the fetched data, allowing more control over data reuse.

3. Final Answer:

   useAsyncData requires a unique key for caching, useFetch does not. -> Option B

4. Quick Check:

   Key caching difference = D [OK]

Hint: Remember: useAsyncData needs a key, useFetch is simpler [OK]

Common Mistakes:

• Thinking useFetch caches data with keys
• Confusing client/server usage of both
• Assuming useAsyncData auto-refreshes data

2. Which of the following is the correct syntax to use useAsyncData in a Nuxt component?

easy

A. const { data } = useAsyncData('posts', () => $fetch('/api/posts'))

B. const data = useAsyncData('/api/posts')

C. useAsyncData(() => $fetch('posts'), 'posts')

D. const { data } = useAsyncData(() => fetch('/api/posts'))

Solution

1. Step 1: Check the required parameters for useAsyncData

   The first parameter is a unique key string, the second is a function returning a promise.

2. Step 2: Validate each option's syntax

   const { data } = useAsyncData('posts', () => $fetch('/api/posts')) correctly uses a key 'posts' and a fetch function with $fetch. Others miss the key or use wrong order.

3. Final Answer:

   const { data } = useAsyncData('posts', () => $fetch('/api/posts')) -> Option A

4. Quick Check:

   Key first, fetch function second = A [OK]

Hint: Key string first, fetch function second in useAsyncData [OK]

Common Mistakes:

• Omitting the key parameter
• Swapping parameters order
• Using native fetch instead of $fetch

3. Given this code snippet in a Nuxt component:

const { data, pending } = useFetch('/api/user')

return { data, pending }

What will pending be initially when the component loads?

medium

A. undefined

B. false

C. true

D. null

Solution

1. Step 1: Understand useFetch loading state

   pending is a reactive boolean indicating if the fetch is still in progress.

2. Step 2: Initial value of pending

   When the component loads and fetch starts, pending is true until data arrives.

3. Final Answer:

   true -> Option C

4. Quick Check:

   Loading state pending = true [OK]

Hint: pending is true while fetching data [OK]

Common Mistakes:

• Assuming pending is false initially
• Confusing pending with data presence
• Expecting pending to be null or undefined

4. You wrote this code in a Nuxt component:

const { data } = useAsyncData(() => $fetch('/api/items'))

But the data never loads. What is the likely problem?

medium

A. Using $fetch instead of native fetch.

B. Returning data directly instead of inside a function.

C. Not awaiting the useAsyncData call.

D. Missing a unique key as the first argument to useAsyncData.

Solution

1. Step 1: Check useAsyncData parameters

   useAsyncData requires a unique key string as the first argument for caching.

2. Step 2: Identify missing key issue

   Omitting the key causes the fetch not to run properly or cache data, so data never loads.

3. Final Answer:

   Missing a unique key as the first argument to useAsyncData. -> Option D

4. Quick Check:

   Key missing in useAsyncData = B [OK]

Hint: Always provide a key string first in useAsyncData [OK]

Common Mistakes:

• Skipping the key argument
• Confusing $fetch with fetch as cause
• Expecting useAsyncData to be awaited

5. You want to fetch user data and posts in a Nuxt page using useAsyncData. You want posts to refresh every time the user ID changes. Which approach correctly achieves this?

hard

A. Use useAsyncData with a key including the user ID, e.g., useAsyncData(`posts-${userId}`, () => $fetch(`/api/posts?user=${userId}`)).

B. Use useAsyncData with a fixed key 'posts' and rely on automatic refresh.

C. Use useFetch instead of useAsyncData because it auto-refreshes on param change.

D. Call useAsyncData without a key and manually watch userId to refetch.

Solution

1. Step 1: Understand caching with keys in useAsyncData

   Keys uniquely identify cached data. Changing the key triggers a new fetch.

2. Step 2: Use dynamic key with user ID

   Including userId in the key string ensures posts refetch when userId changes.

3. Step 3: Evaluate other options

   Fixed keys won't refresh; useFetch doesn't auto-refresh on param change; manual watch is more complex.

4. Final Answer:

   Use useAsyncData with a key including the user ID, e.g., useAsyncData(`posts-${userId}`, () => $fetch(`/api/posts?user=${userId}`)). -> Option A

5. Quick Check:

   Dynamic key triggers refetch = C [OK]

Hint: Include changing params in key string for refetch [OK]

Common Mistakes:

• Using fixed keys expecting auto-refresh
• Assuming useFetch auto-refreshes on param change
• Skipping key causes no caching or refetch