Managing large applications in React - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import a component from a separate file.

React

import [1] from './Header';

function App() {
  return <[1] />;
}

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

AHeader

Bheader

CAppHeader

DheaderComponent

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase names for components in import statements.

Mismatching the component name with the exported name.

React components are imported by their exact exported name, which is usually capitalized.

2fill in blank

medium

Complete the code to create a context for sharing data across components.

React

import { createContext } from 'react';

const UserContext = [1]();

export default UserContext;

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

AuseContext

BuseEffect

CuseState

DcreateContext

Attempts:

3 left

💡 Hint

Common Mistakes

Using useContext instead of createContext to create a context.

Confusing hooks with context creation functions.

createContext() is used to create a new context object in React.

3fill in blank

hard

Fix the error in the code to properly provide context to child components.

React

import UserContext from './UserContext';

function App() {
  const user = { name: 'Alice' };

  return (
    <UserContext.[1] value={user}>
      <Dashboard />
    </UserContext.[1]>
  );
}

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

AConsumer

BProvider

CContext

DWrapper

Attempts:

3 left

💡 Hint

Common Mistakes

Using Consumer instead of Provider to supply context.

Using incorrect component names like Context or Wrapper.

The Provider component is used to supply context values to child components.

4fill in blank

hard

Fill both blanks to correctly use React.lazy and Suspense for code splitting.

React

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

const LazyComponent = [2](() => import('./LazyComponent'));

function App() {
  return (
    <React.Suspense fallback={<div>Loading...</div>}>
      <LazyComponent />
    </React.Suspense>
  );
}

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

Alazy

BuseState

CuseEffect

Dmemo

Attempts:

3 left

💡 Hint

Common Mistakes

Using useState or useEffect instead of lazy for code splitting.

Not importing lazy from React.

React.lazy is used to load components lazily, and it must be imported from React.

5fill in blank

hard

Fill all three blanks to create a custom hook that manages a counter state.

React

import { [1], [2] } from 'react';

function useCounter(initialValue) {
  const [count, setCount] = [3](initialValue);

  const increment = () => setCount(count + 1);

  return { count, increment };
}

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

AuseState

BuseEffect

DuseReducer

Attempts:

3 left

💡 Hint

Common Mistakes

Using useEffect instead of useState for state management.

Not importing useState correctly.

useState is imported and used to create state in a custom hook. useEffect is often imported but not used here, so it's a distractor.

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