Why custom hooks are used in React - Quick Recap

Recall & Review

beginner

What is a custom hook in React?

A custom hook is a JavaScript function that starts with 'use' and lets you reuse stateful logic between components without repeating code.

beginner

Why do developers create custom hooks?

To share and reuse logic easily across multiple components, making code cleaner and easier to maintain.

intermediate

How do custom hooks improve code organization?

They separate complex logic from UI code, so components stay simple and focused on rendering.

intermediate

Can custom hooks use other hooks inside them?

Yes, custom hooks can use built-in hooks like useState or useEffect to manage state and side effects internally.

beginner

Give an example scenario where a custom hook is useful.

When multiple components need to fetch data from the same API and handle loading and error states, a custom hook can manage this logic once and share it.

What is the main reason to use a custom hook in React?

A To reuse stateful logic across components

B To style components

C To create class components

D To write HTML inside JavaScript

Custom hooks help reuse logic like state and effects across components, avoiding code duplication.

Which of these is true about custom hooks?

A They cannot use other hooks

B They can only be used once

C They replace React components

D They must start with 'use'

Custom hooks must start with 'use' so React can identify them as hooks.

Custom hooks help keep components:

A Without any state

B Simple and focused on UI

C Dependent on class syntax

D Long and complex

By moving logic to custom hooks, components stay clean and focused on rendering.

Can a custom hook use useState inside it?

A Yes, it can manage its own state

B No, hooks cannot be nested

C Only if it is a class component

D Only outside React components

Custom hooks can use built-in hooks like useState to manage internal state.

Which naming convention is correct for a custom hook?

A FetchData

B fetchDataHook

C useFetchData

D customHook

Custom hooks must start with 'use' to follow React's rules and conventions.

Explain why custom hooks are useful in React and how they help with code reuse.

Think about how you might share the same behavior in many places without repeating code.

Describe how a custom hook can improve the organization of a React app's code.

Consider how moving logic out of components helps keep things tidy.

Practice

1. Why do React developers create custom hooks?

easy

A. To reuse stateful logic across multiple components

B. To style components with CSS

C. To replace React components entirely

D. To write HTML inside JavaScript

Solution

1. Step 1: Understand the purpose of hooks

   Hooks in React let you use state and other React features without writing a class.

2. Step 2: Identify why custom hooks are made

   Custom hooks let you reuse stateful logic easily across different components, avoiding repetition.

3. Final Answer:

   To reuse stateful logic across multiple components -> Option A

4. Quick Check:

   Custom hooks = reuse logic [OK]

Hint: Custom hooks reuse logic, not styles or HTML [OK]

Common Mistakes:

• Thinking custom hooks are for styling
• Believing custom hooks replace components
• Confusing hooks with HTML syntax

2. Which of the following is the correct way to name a custom hook in React?

easy

A. useFetchData

B. fetchDataHook

C. FetchData

D. hookUseFetch

Solution

1. Step 1: Recall React naming conventions for hooks

   React requires custom hooks to start with the word 'use' to identify them as hooks.

2. Step 2: Check each option

   Only 'useFetchData' starts with 'use', following React's convention.

3. Final Answer:

   useFetchData -> Option A

4. Quick Check:

   Custom hook names start with 'use' [OK]

Hint: Custom hooks always start with 'use' [OK]

Common Mistakes:

• Not starting the name with 'use'
• Using camel case without 'use' prefix
• Confusing component names with hook names

3. What will be the output of this React component using a custom hook?

function useCounter() {
  const [count, setCount] = React.useState(0);
  React.useEffect(() => {
    const timer = setInterval(() => setCount(c => c + 1), 1000);
    return () => clearInterval(timer);
  }, []);
  return count;
}

function Counter() {
  const count = useCounter();
  return 
{count}
;
}

medium

A. Throws an error because hooks can't be used here

B. Always shows 0 and never changes

C. A number that increases by 1 every second starting from 0

D. Shows a static string 'count'

Solution

1. Step 1: Analyze the custom hook useCounter

   It initializes count to 0 and sets up a timer to increase count by 1 every second.

2. Step 2: Understand the component output

   The Counter component uses useCounter and displays the count, which updates every second.

3. Final Answer:

   A number that increases by 1 every second starting from 0 -> Option C

4. Quick Check:

   useCounter returns incrementing count [OK]

Hint: Custom hooks can return changing state values [OK]

Common Mistakes:

• Thinking count stays 0 forever
• Believing hooks can't be used in functions
• Assuming output is a string, not a number

4. Identify the error in this custom hook usage:

function useData() {
  const [data, setData] = React.useState(null);
  fetch('https://api.example.com/data')
    .then(res => res.json())
    .then(json => setData(json));
  return data;
}

function App() {
  const data = useData();
  return <div>{JSON.stringify(data)}</div>;
}

medium

A. Custom hooks cannot return data

B. The fetch call should be inside useEffect to avoid infinite loops

C. useState is used incorrectly and should be replaced with useRef

D. The component should not call the custom hook

Solution

1. Step 1: Check where fetch is called in useData

   fetch is called directly inside the hook body, causing it to run on every render, leading to infinite loops.

2. Step 2: Correct usage with useEffect

   fetch should be inside a useEffect with an empty dependency array to run only once on mount.

3. Final Answer:

   The fetch call should be inside useEffect to avoid infinite loops -> Option B

4. Quick Check:

   Side effects go inside useEffect [OK]

Hint: Put side effects like fetch inside useEffect [OK]

Common Mistakes:

• Calling fetch directly in hook body
• Misusing useState instead of useEffect
• Thinking hooks can't return values

5. You want to share logic for fetching user data and managing loading state across several components. Which approach best uses custom hooks to solve this?

hard

A. Store user data in a global variable outside React

B. Write the fetch logic separately in each component to avoid dependencies

C. Use a class component instead of hooks for shared logic

D. Create a custom hook that fetches user data and returns both data and loading state

Solution

1. Step 1: Understand the need for reusable logic

   Fetching data and managing loading state is stateful logic that can be reused with a custom hook.

2. Step 2: Evaluate options for sharing logic

   Creating a custom hook that returns data and loading state allows multiple components to share this logic cleanly.

3. Final Answer:

   Create a custom hook that fetches user data and returns both data and loading state -> Option D

4. Quick Check:

   Custom hooks share stateful logic best [OK]

Hint: Custom hooks bundle related state and logic for reuse [OK]

Common Mistakes:

• Duplicating fetch code in every component
• Using class components instead of hooks
• Using global variables that break React's state flow