Managing large applications in React - Cheat Sheet & Quick Revision

Recall & Review

beginner

Why is it important to split a large React app into smaller components?

Splitting a large app into smaller components makes the code easier to understand, test, and maintain. It also helps reuse parts of the UI and improves performance by updating only needed parts.

intermediate

What is code splitting in React and why use it?

Code splitting means breaking the app’s code into smaller chunks that load only when needed. This speeds up the initial load time and improves user experience by not loading everything at once.

intermediate

How does React Context help in managing state in large applications?

React Context allows sharing data like user info or theme across many components without passing props down manually at every level. This reduces 'prop drilling' and keeps state management cleaner.

intermediate

What role do custom hooks play in large React apps?

Custom hooks let you extract and reuse logic across components. This keeps code DRY (Don’t Repeat Yourself) and makes complex behaviors easier to manage and test.

beginner

Why is folder structure important in large React applications?

A clear folder structure helps developers find and organize files easily. It reduces confusion, speeds up development, and makes teamwork smoother.

What is the main benefit of using React.lazy and Suspense?

A To split code and load components only when needed

B To style components with CSS

C To manage global state

D To create class components

React.lazy and Suspense help load components lazily, improving app performance by loading code only when needed.

Which React feature helps avoid passing props through many layers?

A Context API

B useState

C useEffect

D React Router

Context API allows sharing data across components without passing props manually through every level.

What is a good reason to create custom hooks in a React app?

A To write CSS styles

B To create new HTML elements

C To manage routing

D To reuse logic across components

Custom hooks let you reuse logic, making code cleaner and easier to maintain.

How does a good folder structure help in large React apps?

A It makes the app run faster

B It helps organize files and find code easily

C It changes the app’s colors

D It automatically fixes bugs

A clear folder structure helps developers organize and locate files quickly, improving teamwork and maintenance.

What does 'prop drilling' mean in React?

A Deleting unused props

B Using props only once

C Passing props through many component layers unnecessarily

D Creating props dynamically

'Prop drilling' is when you pass props through many layers of components even if intermediate components don’t need them.

Explain how you would organize a large React application to keep it maintainable and efficient.

Think about how to keep code easy to understand, share data, and load fast.

Describe the benefits of using React Context and code splitting in large applications.

Focus on state sharing and performance improvements.

Practice

1. What is a common way to organize a large React application to keep it manageable?

easy

A. Use only class components to keep consistency

B. Write all code in a single file for easy access

C. Avoid using components and write plain JavaScript

D. Split the app into smaller components and folders

Solution

1. Step 1: Understand component-based design

   React encourages breaking UI into small, reusable components.

2. Step 2: Organize code in folders

   Grouping related components and files in folders helps maintain large apps.

3. Final Answer:

   Split the app into smaller components and folders -> Option D

4. Quick Check:

   Component + folder structure = A [OK]

Hint: Think modular: small parts in folders make apps manageable [OK]

Common Mistakes:

• Putting all code in one file makes it hard to maintain
• Ignoring components loses React's main advantage
• Using only class components is outdated

2. Which of the following is the correct way to import a component named Header from a file in React?

easy

A. import Header from './Header';

B. require Header from './Header';

C. import { Header } from './Header.js';

D. include Header from './Header';

Solution

1. Step 1: Recognize ES6 import syntax

   React uses ES6 modules, so import Header from './Header'; is correct for default exports.

2. Step 2: Check other options

   require is CommonJS, not standard in React apps; include is invalid; named import { Header } requires named export.

3. Final Answer:

   import Header from './Header'; -> Option A

4. Quick Check:

   Default import uses import X from [OK]

Hint: Use ES6 import syntax: import Component from 'path' [OK]

Common Mistakes:

• Using require instead of import in React
• Confusing default and named imports
• Using invalid keywords like include

3. Given this React component structure:

src/
  components/
    Navbar.js
  pages/
    Home.js
    About.js
  App.js

Which statement best describes how routing helps manage this app?

medium

A. Routing allows switching between Home and About pages without reloading

B. Routing bundles all components into one file for faster loading

C. Routing automatically converts components to class components

D. Routing disables navigation to keep app simple

Solution

1. Step 1: Understand routing purpose

   Routing lets users move between different views (pages) in a React app without full page reloads.

2. Step 2: Apply to given structure

   Home.js and About.js are pages; routing switches between them smoothly.

3. Final Answer:

   Routing allows switching between Home and About pages without reloading -> Option A

4. Quick Check:

   Routing = page switching without reload [OK]

Hint: Routing changes views without refreshing the whole page [OK]

Common Mistakes:

• Thinking routing bundles files together
• Believing routing changes component types
• Assuming routing disables navigation

4. You have this React code snippet:

function App() {
  const [count, setCount] = useState(0)

  return (
    <div>
      <button onClick="setCount(count + 1)">Increment</button>
      <p>Count: {count}</p>
    </div>
  )
}

What is the main error preventing the button from working?

medium

A. setCount should be called without parentheses

B. Missing import of React

C. Using double quotes instead of curly braces for onClick handler

D. State variable count is not initialized

Solution

1. Step 1: Check onClick syntax

   In JSX, event handlers must be passed as functions inside curly braces, not strings in quotes.

2. Step 2: Identify the error

   Here, onClick="setCount(count + 1)" uses quotes, so React treats it as a string, not a function.

3. Final Answer:

   Using double quotes instead of curly braces for onClick handler -> Option C

4. Quick Check:

   JSX event handlers need curly braces [OK]

Hint: Use curly braces for event handlers, not quotes [OK]

Common Mistakes:

• Using quotes instead of curly braces for onClick
• Forgetting to import React (less common in new versions)
• Calling setCount incorrectly

5. In a large React app, you want to keep UI components separate from business logic for easier teamwork. Which approach best supports this?

hard

A. Avoid using hooks and manage state globally only

B. Use container components to handle logic and presentational components for UI

C. Write all logic inside UI components to keep code together

D. Put all components and logic in one file to reduce imports

Solution

1. Step 1: Understand separation of concerns

   Separating UI and logic helps teams work independently and keeps code clean.

2. Step 2: Apply container and presentational pattern

   Container components manage data and logic; presentational components focus on UI rendering.

3. Final Answer:

   Use container components to handle logic and presentational components for UI -> Option B

4. Quick Check:

   Separate logic and UI with containers and presentational components [OK]

Hint: Split logic (containers) and UI (presentational) components [OK]

Common Mistakes:

• Mixing logic inside UI components makes maintenance hard
• Avoiding hooks limits React's power
• Putting everything in one file causes confusion