React ecosystem overview - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the React library in a functional component.

React

import [1] from 'react';

function MyComponent() {
  return <div>Hello React!</div>;
}

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

AComponent

BReact

CuseState

Drender

Attempts:

3 left

💡 Hint

Common Mistakes

Using named imports like 'Component' instead of default import.

Forgetting to import React at all.

You import the main React object using import React from 'react'; to use React features in your component.

2fill in blank

medium

Complete the code to declare a state variable using React hooks.

React

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

function Counter() {
  const [count, setCount] = [1](0);
  return <button>{count}</button>;
}

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

AuseState

BuseEffect

CuseContext

DuseRef

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'useEffect' instead of 'useState'.

Not destructuring the array returned by the hook.

The useState hook lets you add state to functional components.

3fill in blank

hard

Fix the error in the code to correctly use the useEffect hook for side effects.

React

import React, { useEffect } from 'react';

function Logger() {
  useEffect(() => {
    console.log('Component mounted');
  }, [1]);
  return <div>Check console</div>;
}

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

A{}

Bnull

C[]

Dtrue

Attempts:

3 left

💡 Hint

Common Mistakes

Passing an object or null instead of an array.

Omitting the second argument causing effect to run on every render.

Passing an empty array [] as the second argument to useEffect runs the effect only once after the component mounts.

4fill in blank

hard

Fill both blanks to create a context and provide it to child components.

React

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

const ThemeContext = createContext('light');

function App() {
  return (
    <ThemeContext.Provider value=[2]>
      <Child />
    </ThemeContext.Provider>
  );
}

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

AuseContext

B'dark'

C'light'

DuseState

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'useState' instead of 'useContext'.

Providing the wrong value string to the provider.

You import useContext to consume context later, and provide a value like 'dark' to the provider.

5fill in blank

hard

Fill all three blanks to create a memoized callback that updates state.

React

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

function Counter() {
  const [count, setCount] = useState(0);
  const increment = useCallback(() => {
    setCount(count [2] 1);
  }, [[3]]);
  return <button onClick={increment}>{count}</button>;
}

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

AuseEffect

B+

Ccount

DuseMemo

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' instead of '+'.

Leaving dependency array empty causing stale closures.

Importing wrong hooks.

useMemo is imported but not needed here; the correct hook to memoize is useCallback. The increment function adds 1 to count using +, and the dependency array includes count.

Practice

1. Which of the following is NOT typically part of the React ecosystem?

easy

A. Express.js for backend server

B. Redux for state management

C. React Router for navigation

D. Styled Components for styling

Solution

1. Step 1: Identify React ecosystem tools

   React ecosystem includes tools like React Router, Redux, and Styled Components for frontend tasks.

2. Step 2: Recognize backend tools

   Express.js is a backend server framework, not part of React's frontend ecosystem.

3. Final Answer:

   Express.js for backend server -> Option A

4. Quick Check:

   Backend server ≠ React ecosystem [OK]

Hint: React ecosystem focuses on frontend tools, not backend servers [OK]

Common Mistakes:

• Confusing backend frameworks as React tools
• Thinking Redux is not part of React ecosystem
• Assuming all JavaScript libraries belong to React

2. Which syntax correctly imports the useState hook from React?

easy

A. import React.useState from 'react';

B. import useState from 'react';

C. const useState = require('react');

D. import { useState } from 'react';

Solution

1. Step 1: Recall ES module import syntax

   Named imports use curly braces: import { useState } from 'react';.

2. Step 2: Identify incorrect forms

   Default import without braces, require syntax, and dot notation in import are invalid here.

3. Final Answer:

   import { useState } from 'react'; -> Option D

4. Quick Check:

   Named import uses braces [OK]

Hint: Use curly braces for named imports like useState [OK]

Common Mistakes:

• Omitting curly braces for named imports
• Using CommonJS require in ES modules
• Trying to import with dot notation

3. What will be the output of this React component when rendered?

import React, { useState } from 'react';

function Counter() {
  const [count, setCount] = useState(0);
  return (
    <div>
      <p>Count: {count}</p>
      <button onClick={() => setCount(count + 1)}>Increment</button>
    </div>
  );
}

medium

A. Displays 'Count: 0' and increments count on button click

B. Displays 'Count: 1' initially and increments on click

C. Throws an error because useState is not imported

D. Button does nothing when clicked

Solution

1. Step 1: Analyze initial state value

   useState(0) sets count to 0 initially, so 'Count: 0' shows first.

2. Step 2: Understand button click behavior

   Clicking button calls setCount(count + 1), increasing count by 1 each click.

3. Final Answer:

   Displays 'Count: 0' and increments count on button click -> Option A

4. Quick Check:

   Initial state 0, button updates count [OK]

Hint: Initial useState value sets starting count [OK]

Common Mistakes:

• Assuming count starts at 1
• Forgetting to import useState
• Thinking button does not update state

4. Identify the error in this React Router usage:

import { BrowserRouter, Route } from 'react-router-dom';

function App() {
  return (
    <BrowserRouter>
      <Route path='/home' component={Home} />
    </BrowserRouter>
  );
}

medium

A. The path prop must be inside a Switch component

B. BrowserRouter must wrap only one child element

C. Route should use 'element' prop with JSX, not 'component' prop

D. Home component must be imported from 'react-router-dom'

Solution

1. Step 1: Check React Router v6 syntax

   In React Router v6, Route uses element prop with JSX, not component.

2. Step 2: Validate other props and components

   BrowserRouter can wrap multiple children; Switch is replaced by Routes; Home is user-defined, not from react-router-dom.

3. Final Answer:

   Route should use 'element' prop with JSX, not 'component' prop -> Option C

4. Quick Check:

   React Router v6 uses element prop [OK]

Hint: Use element={} in Route for React Router v6 [OK]

Common Mistakes:

• Using component prop instead of element
• Expecting Switch component in v6
• Importing user components from react-router-dom

5. You want to fetch data from an API and style the results using the React ecosystem. Which combination of tools fits best?

hard

A. Redux for data fetching and CSS Modules for styling

B. React Query for data fetching and Tailwind CSS for styling

C. React Router for data fetching and Styled Components for styling

D. Axios for styling and React Context for data fetching

Solution

1. Step 1: Identify data fetching tools in React ecosystem

   React Query is a popular library for fetching and caching API data in React apps.

2. Step 2: Identify styling tools

   Tailwind CSS is a utility-first CSS framework commonly used with React for styling.

3. Final Answer:

   React Query for data fetching and Tailwind CSS for styling -> Option B

4. Quick Check:

   React Query + Tailwind CSS = best fit [OK]

Hint: React Query handles data; Tailwind CSS handles styling [OK]

Common Mistakes:

• Using Redux for data fetching only
• Confusing React Router as data fetch tool
• Mixing styling and data fetching roles