Single Page Application concept in React - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a React component that returns a simple heading.

React

function Welcome() {
  return <h1>[1]</h1>;
}

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

AHello, SPA!

B<h1>Hello, SPA!</h1>

C{Hello, SPA!}

D"Hello, SPA!"

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting quotes around the string

Returning raw text without JSX tags

The component must return JSX with a string inside the <h1> tags. The string must be in quotes but without extra braces.

2fill in blank

medium

Complete the code to import React's useState hook for managing component state.

React

import React, [1] from 'react';

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

AuseEffect

BuseContext

CuseState

DuseRef

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing useState with useEffect

Forgetting to import the hook

useState is the hook used to add state to functional components in React.

3fill in blank

hard

Fix the error in the code to correctly update state on button click.

React

const [count, setCount] = useState(0);

function increment() {
  setCount([1]);
}

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

Acount + 1

Bcount++

C++count

Dcount += 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using count++ which returns the old value

Trying to modify state directly

State updates must use the new value directly. Using count + 1 returns the incremented value correctly.

4fill in blank

hard

Fill both blanks to create a simple SPA navigation using React Router.

React

import { BrowserRouter as [1], Route, Routes } from 'react-router-dom';

function App() {
  return (
    <[2]>
      <Routes>
        <Route path="/" element={<Home />} />
      </Routes>
    </[2]>
  );
}

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

ARouter

BRouterProvider

CBrowserRouter

DSwitch

Attempts:

3 left

💡 Hint

Common Mistakes

Using Switch which is deprecated in React Router v6

Confusing Router with BrowserRouter

BrowserRouter is the component that enables SPA navigation in React Router v6.

5fill in blank

hard

Fill all three blanks to create a React component that fetches data on mount and shows loading state.

React

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

function DataFetcher() {
  const [data, setData] = useState(null);
  const [loading, setLoading] = useState(true);

  [2](() => {
    fetch('/api/data')
      .then(res => res.json())
      .then(json => {
        setData(json);
        setLoading(false);
      });
  }, [3]);

  if (loading) return <p>Loading...</p>;
  return <pre>{JSON.stringify(data, null, 2)}</pre>;
}

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

AuseEffect

B[]

C[ ]

DuseMemo

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to import useEffect

Passing no dependency array causing infinite loops

Using useMemo instead of useEffect

useEffect runs code on mount. The empty array [] as dependency means it runs only once.

Practice

1. What is the main advantage of a Single Page Application (SPA) compared to traditional multi-page websites?

easy

A. It uses only server-side rendering without JavaScript.

B. It loads the page once and updates content dynamically without full reloads.

C. It requires a new page load for every user action.

D. It does not support navigation between different views.

Solution

1. Step 1: Understand SPA behavior

   SPAs load a single HTML page and dynamically update content without reloading the entire page.

2. Step 2: Compare with traditional websites

   Traditional sites reload the whole page on navigation, causing slower user experience.

3. Final Answer:

   It loads the page once and updates content dynamically without full reloads. -> Option B

4. Quick Check:

   SPA = dynamic content update without reload [OK]

Hint: SPAs avoid full page reloads for faster user experience [OK]

Common Mistakes:

• Thinking SPAs reload pages on every action
• Confusing SPAs with server-only rendering
• Believing SPAs don't support navigation

2. Which React library is commonly used to manage navigation and URL paths in a Single Page Application?

easy

A. Styled Components

B. Redux

C. Axios

D. React Router

Solution

1. Step 1: Identify navigation management in React

   React Router is designed to handle routing and URL paths in SPAs.

2. Step 2: Differentiate other libraries

   Redux manages state, Axios handles HTTP requests, Styled Components manage styling.

3. Final Answer:

   React Router -> Option D

4. Quick Check:

   Routing in React SPA = React Router [OK]

Hint: React Router controls SPA navigation and URLs [OK]

Common Mistakes:

• Confusing Redux with routing
• Thinking Axios manages navigation
• Assuming styling libraries handle routing

3. Given this React SPA code snippet using React Router:

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

function App() {
  return (
    <BrowserRouter>
      <Routes>
        <Route path='/' element=<Home /> />
        <Route path='/about' element=<About /> />
      </Routes>
    </BrowserRouter>
  );
}

What happens when the user navigates to /about URL?

medium

A. Nothing happens because routes are not defined correctly.

B. The browser reloads the entire page and shows About component.

C. The About component renders without a full page reload.

D. The Home component renders instead of About.

Solution

1. Step 1: Analyze React Router setup

   The Route with path '/about' renders the About component inside BrowserRouter.

2. Step 2: Understand SPA navigation

   React Router updates the view without reloading the whole page when navigating to '/about'.

3. Final Answer:

   The About component renders without a full page reload. -> Option C

4. Quick Check:

   React Router navigation = no full reload [OK]

Hint: React Router changes views without reloading page [OK]

Common Mistakes:

• Assuming full page reload on route change
• Thinking routes are not matched correctly
• Confusing Home and About components

4. Identify the error in this React SPA routing code:

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

function App() {
  return (
    <BrowserRouter>
      <Routes>
        <Route path='/' component={Home} />
        <Route path='/profile' element=<Profile /> />
      </Routes>
    </BrowserRouter>
  );
}

medium

A. The first Route uses 'component' prop instead of 'element'.

B. The BrowserRouter is missing a closing tag.

C. Routes should be replaced with Switch.

D. Profile component is not imported.

Solution

1. Step 1: Check Route props

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

2. Step 2: Verify other code parts

   BrowserRouter is properly closed, Routes is correct in v6, and Profile import is not shown but not necessarily an error here.

3. Final Answer:

   The first Route uses 'component' prop instead of 'element'. -> Option A

4. Quick Check:

   React Router v6 Route uses element prop [OK]

Hint: Use 'element' prop with JSX in React Router v6 [OK]

Common Mistakes:

• Using 'component' prop from older React Router versions
• Confusing Routes with Switch in v6
• Assuming missing closing tags without checking

5. You want to build a React SPA that shows a loading spinner while fetching user data on route change. Which approach best fits SPA principles?

hard

A. Use React Router for routes and show a spinner component while fetching data asynchronously in the route component.

B. Reload the entire page on each route change to fetch fresh data.

C. Fetch all user data once on app load and never update it.

D. Use multiple HTML pages and link between them for each user view.

Solution

1. Step 1: Understand SPA data fetching

   SPAs fetch data asynchronously and update views without full reloads.

2. Step 2: Implement loading state in route components

   Showing a spinner while fetching data fits SPA dynamic update and user feedback.

3. Step 3: Eliminate non-SPA approaches

   Reloading pages or using multiple HTML pages breaks SPA flow; fetching once without updates is inflexible.

4. Final Answer:

   Use React Router for routes and show a spinner component while fetching data asynchronously in the route component. -> Option A

5. Quick Check:

   SPA + async data + spinner = Use React Router for routes and show a spinner component while fetching data asynchronously in the route component. [OK]

Hint: Show spinner during async fetch inside SPA route components [OK]

Common Mistakes:

• Reloading pages instead of dynamic updates
• Not showing loading feedback during fetch
• Ignoring SPA dynamic data needs