Custom hook best practices in React - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a custom hook that uses React's useState.

React

import { useState } from 'react';

function useCounter() {
  const [count, setCount] = [1](0);
  return [count, setCount];
}

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

AuseEffect

BuseRef

CuseContext

DuseState

Attempts:

3 left

💡 Hint

Common Mistakes

Using useEffect instead of useState for state management.

Trying to use useRef to hold state that triggers re-render.

The useState hook is used to add state to a custom hook.

2fill in blank

medium

Complete the code to ensure the custom hook returns a memoized callback.

React

import { useCallback } from 'react';

function useLogger() {
  const log = [1](() => {
    console.log('Logging');
  }, []);
  return log;
}

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

AuseCallback

BuseMemo

CuseEffect

DuseState

Attempts:

3 left

💡 Hint

Common Mistakes

Using useMemo instead of useCallback for functions.

Not memoizing the function causing unnecessary re-renders.

useCallback memoizes a function so it does not get recreated on every render.

3fill in blank

hard

Fix the error in the custom hook by completing the missing import.

React

function useWindowWidth() {
  const [width, setWidth] = useState(window.innerWidth);

  useEffect(() => {
    function handleResize() {
      setWidth(window.innerWidth);
    }
    window.addEventListener('resize', handleResize);
    return () => window.removeEventListener('resize', handleResize);
  }, []);

  return width;
}

export default useWindowWidth;

// Missing import: import [1] from 'react';

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

AuseEffect

BuseState

CuseCallback

DuseRef

Attempts:

3 left

💡 Hint

Common Mistakes

Importing useEffect but forgetting useState.

Not importing any hooks causing runtime errors.

The hook uses useState but it was not imported. Importing it fixes the error.

4fill in blank

hard

Fill both blanks to create a custom hook that fetches data and stores loading state.

React

import { useState, [1] } from 'react';

function useFetch(url) {
  const [data, setData] = useState(null);
  const [loading, setLoading] = [2](true);

  // fetching logic here
}

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

AuseEffect

BuseState

CuseCallback

DuseRef

Attempts:

3 left

💡 Hint

Common Mistakes

Using useCallback instead of useEffect for fetching.

Not initializing loading state with useState.

useEffect is used to run side effects like fetching data, and useState manages loading state.

5fill in blank

hard

Fill all three blanks to create a custom hook that toggles a boolean state.

React

import { useState } from 'react';

function useToggle(initialValue = false) {
  const [value, setValue] = useState([1]);
  const toggle = () => setValue([2] => ![3]);
  return [value, toggle];
}

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

Atrue

Bprev

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Initializing with true instead of false.

Not using the previous state in the toggle function.

Initialize state with false. The toggle function uses the previous state prev to invert the value.

Practice

1. Which of the following is a best practice when naming a custom React hook?

easy

A. Start the hook name with use to follow React conventions

B. Name the hook with a capital letter but no prefix

C. Use any name as long as it describes the functionality

D. Prefix the hook name with hook instead of use

Solution

1. Step 1: Understand React hook naming conventions

   React requires custom hooks to start with use so React can identify them as hooks.

2. Step 2: Evaluate the options

   Only Start the hook name with use to follow React conventions correctly follows this convention by starting the name with use.

3. Final Answer:

   Start the hook name with use to follow React conventions -> Option A

4. Quick Check:

   Hook names start with 'use' = B [OK]

Hint: Always start custom hook names with 'use' [OK]

Common Mistakes:

• Naming hooks without 'use' prefix
• Using 'hook' prefix instead of 'use'
• Starting hook names with lowercase letters without 'use'

2. Which of the following is the correct syntax to define a custom hook that returns a count state and an increment function?

easy

A. function useCount() { const [count, setCount] = useState(0); return { count increment: () => setCount(count + 1) }; }

B. function countHook() { const [count, setCount] = useState(0); return [count, () => setCount(count + 1)]; }

C. function useCount() { const [count, setCount] = useState(0); return [count, () => setCount(count + 1)]; }

D. function useCount() { const count = 0; function increment() { count += 1; } return { count, increment }; }

Solution

1. Step 1: Check the hook naming and return type

   The hook must start with use and return state and updater properly. function useCount() { const [count, setCount] = useState(0); return [count, () => setCount(count + 1)]; } uses useCount and returns an array with count and increment function.

2. Step 2: Verify state management correctness

   function useCount() { const [count, setCount] = useState(0); return [count, () => setCount(count + 1)]; } uses useState correctly and returns a function that updates state with setCount(count + 1). This is the correct pattern.

3. Final Answer:

   function useCount() { const [count, setCount] = useState(0); return [count, () => setCount(count + 1)]; } -> Option C

4. Quick Check:

   Custom hook syntax with useState and return array = C [OK]

Hint: Custom hooks return state and updater, named starting with 'use' [OK]

Common Mistakes:

• Not starting function name with 'use'
• Returning object instead of array without reason
• Not using useState for state management
• Mutating state directly instead of using setter

3. Given this custom hook code:

function useToggle(initial) {
  const [on, setOn] = useState(initial);
  const toggle = () => setOn(prev => !prev);
  return [on, toggle];
}

function Component() {
  const [isOn, toggle] = useToggle(false);
  toggle();
  return 
{isOn ? 'ON' : 'OFF'}
;
}

What will the component render after calling toggle() once?

medium

A. ON

B. false

C. OFF

D. Error because toggle is called outside an event

Solution

1. Step 1: Analyze where toggle is called

   toggle() is called directly in the component body, which executes during every render phase.

2. Step 2: Understand React render rules

   State updates during render trigger re-renders. Since toggle() is unconditional, it flips state every render, causing an infinite loop. React prohibits this and produces errors/warnings (e.g., "Cannot update a component while rendering a different component" or too many re-renders).

3. Final Answer:

   Error because toggle is called outside an event -> Option D

4. Quick Check:

   State updaters only in events/effects, not render body [OK]

Hint: Never call state updaters during render; use events or useEffect [OK]

Common Mistakes:

• Assuming async update shows initial state without considering re-render loop
• Expecting 'ON' due to toggle flip
• Confusing boolean with string output
• Thinking render body calls are safe without infinite loop

4. What is wrong with this custom hook code?

function useCounter() {
  let count = 0;
  const increment = () => { count += 1; };
  return { count, increment };
}

medium

A. It does not use React state, so count won't trigger re-renders

B. The hook name should not start with 'use'

C. The increment function should not modify count

D. It should return an array, not an object

Solution

1. Step 1: Check state management in the hook

   The hook uses a local variable count that resets to 0 on every call. It does not use useState, so React won't track changes or re-render.

2. Step 2: Understand React state importance

   Without useState, updating count does not cause component updates, making the hook ineffective.

3. Final Answer:

   It does not use React state, so count won't trigger re-renders -> Option A

4. Quick Check:

   Local variable won't update UI without useState [OK]

Hint: Always use useState for reactive state in hooks [OK]

Common Mistakes:

• Using local variables instead of useState
• Expecting UI to update without state
• Returning object instead of array (not always wrong)
• Misnaming hook without 'use' prefix

5. You want to create a custom hook useFetch that fetches data from a URL and returns loading state, data, and error. Which approach follows best practices?

hard

A. Fetch data directly in the hook body without useEffect, return data and error only

B. Use useEffect inside the hook to fetch data on mount, use useState for loading, data, and error, and return them as an object

C. Use useMemo to fetch data and return loading and data states

D. Fetch data outside the hook and pass it as a parameter to the hook

Solution

1. Step 1: Understand data fetching in hooks

   Fetching data should happen inside useEffect to avoid running on every render. State variables track loading, data, and error.

2. Step 2: Evaluate options for best practice

   Use useEffect inside the hook to fetch data on mount, use useState for loading, data, and error, and return them as an object correctly uses useEffect and useState to manage asynchronous fetch and returns all relevant states as an object for clarity.

3. Final Answer:

   Use useEffect inside the hook to fetch data on mount, use useState for loading, data, and error, and return them as an object -> Option B

4. Quick Check:

   Fetch in useEffect with state management = A [OK]

Hint: Fetch inside useEffect, manage state with useState [OK]

Common Mistakes:

• Fetching data directly in hook body causing infinite loops
• Not managing loading or error states
• Using useMemo for side effects
• Passing fetched data as parameter instead of fetching inside hook