Custom hook best practices in React - Mini Project: Build & Apply

Custom Hook Best Practices in React

📖 Scenario: You are building a React app that fetches user data from an API. To keep your code clean and reusable, you want to create a custom hook that handles fetching and loading state.

🎯 Goal: Build a custom React hook called useUserData that fetches user data from a URL, manages loading state, and returns the data and loading status. Then use this hook in a functional component to display the user name or a loading message.

📋 What You'll Learn

Create a state variable to hold user data

Create a state variable to hold loading status

Use useEffect to fetch data from https://jsonplaceholder.typicode.com/users/1

Return the user data and loading status from the custom hook

Use the custom hook in a component to show loading or user name

💡 Why This Matters

🌍 Real World

Custom hooks help keep React code clean and reusable, especially for common tasks like data fetching.

💼 Career

Understanding custom hooks is essential for React developers to write maintainable and scalable applications.

1

Set up state variables in the custom hook

Create a custom hook called useUserData. Inside it, create a state variable called user initialized to null and a state variable called loading initialized to true using useState.

React

import { useState, useEffect } from 'react';

function useUserData() {
  // Create user state variable initialized to null
  // Create loading state variable initialized to true
  // Your code here
}

Hint

Use useState(null) for user and useState(true) for loading.

2

Add useEffect to fetch user data

Inside the useUserData hook, add a useEffect that fetches data from https://jsonplaceholder.typicode.com/users/1. When the data is received, update user with the JSON response and set loading to false. Use an empty dependency array [] so it runs once.

React

import { useState, useEffect } from 'react';

function useUserData() {
  const [user, setUser] = useState(null);
  const [loading, setLoading] = useState(true);

  // Add useEffect to fetch user data
  // Your code here
}

Hint

Use fetch inside useEffect and update states inside then.

3

Return user and loading from the custom hook

At the end of the useUserData hook, return an object with user and loading properties.

React

import { useState, useEffect } from 'react';

function useUserData() {
  const [user, setUser] = useState(null);
  const [loading, setLoading] = useState(true);

  useEffect(() => {
    fetch('https://jsonplaceholder.typicode.com/users/1')
      .then(response => response.json())
      .then(data => {
        setUser(data);
        setLoading(false);
      });
  }, []);

  // Return user and loading
  // Your code here
}

Hint

Return an object with user and loading.

4

Use the custom hook in a component

Create a functional component called UserProfile. Inside it, call the useUserData hook to get user and loading. If loading is true, return a <p> with text "Loading...". Otherwise, return a <p> showing the user's name from user.name.

React

import { useState, useEffect } from 'react';

function useUserData() {
  const [user, setUser] = useState(null);
  const [loading, setLoading] = useState(true);

  useEffect(() => {
    fetch('https://jsonplaceholder.typicode.com/users/1')
      .then(response => response.json())
      .then(data => {
        setUser(data);
        setLoading(false);
      });
  }, []);

  return { user, loading };
}

// Create UserProfile component below
// Your code here

Hint

Call the hook, check loading, and show user name inside a paragraph.

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