Composable for API calls (useFetch pattern) in Vue - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Vue Composition API function needed to create reactive references.

Vue

import { [1] } from 'vue';

Drag options to blanks, or click blank then click option'

Areactive

Bref

Ccomputed

Dwatch

Attempts:

3 left

💡 Hint

Common Mistakes

Using reactive instead of ref for simple values.

Importing computed or watch which serve different purposes.

The ref function creates a reactive reference, which is essential for storing reactive data like API responses.

2fill in blank

medium

Complete the code to define the composable function that fetches data from an API.

Vue

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

  async function fetchData() {
    try {
      const response = await fetch([1]);
      data.value = await response.json();
    } catch (err) {
      error.value = err;
    }
  }

  fetchData();

  return { data, error };
}

Drag options to blanks, or click blank then click option'

Aurl

BfetchData

Cdata

Derror

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the data ref instead of the URL string.

Using the function name or error ref as the fetch argument.

The fetch function needs the URL string to make the API call, which is passed as the url parameter.

3fill in blank

hard

Fix the error in the code by completing the line that returns the reactive data and error from the composable.

Vue

return { [1] };

Drag options to blanks, or click blank then click option'

Adata, error

Bdata.error

Cdata; error

Ddata error

Attempts:

3 left

💡 Hint

Common Mistakes

Using dot notation which is invalid here.

Separating variables with semicolons or spaces instead of commas.

Returning an object with data and error properties allows components to access both reactive references.

4fill in blank

hard

Fill both blanks to create a reactive reference and initialize it with null.

Vue

const [1] = [2](null);

Drag options to blanks, or click blank then click option'

Aref

Breactive

Cdata

Derror

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping variable name and function.

Using reactive instead of ref for simple values.

data is the variable name holding the reactive reference created by ref initialized with null.

5fill in blank

hard

Fill all three blanks to handle errors reactively and return both data and error from the composable.

Vue

const [1] = [2](null);

return { [3], error };

Drag options to blanks, or click blank then click option'

Adata

Bref

Derror

Attempts:

3 left

💡 Hint

Common Mistakes

Returning undefined variables.

Mixing up variable names and functions.

We create a reactive data reference using ref and return it along with error so components can react to both.

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