What is JSX in React - Interactive Quiz & Practice

Practice - 5 Tasks

1fill in blank

easy

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

React

function Hello() {
  return ([1]);
}

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

Aconsole.log('Hello, world!')

B"Hello, world!"

C<h1>Hello, world!</h1>

DReact.createElement('h1', null, 'Hello, world!')

Attempts:

3 left

💡 Hint

Common Mistakes

Returning a string instead of JSX

Using console.log inside return

Using React.createElement instead of JSX here

JSX looks like HTML inside JavaScript. Here, <h1>Hello, world!</h1> is JSX that React understands and renders as a heading.

2fill in blank

medium

Complete the JSX code to display a paragraph with the text 'Welcome to React!'.

React

const element = [1];

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

A{Welcome to React!}

B"Welcome to React!"

CReact.createElement('p', null, 'Welcome to React!')

D<p>Welcome to React!</p>

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes without tags

Using curly braces without tags

Using React.createElement instead of JSX here

JSX uses HTML-like tags. Here, <p>Welcome to React!</p> is the correct JSX to create a paragraph element.

3fill in blank

hard

Fix the error in this JSX code by completing the blank.

React

const element = <div>[1]Hello</div>;

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

A{' '}

B' '

C" "

D<br/>

Attempts:

3 left

💡 Hint

Common Mistakes

Using plain quotes inside JSX tags

Using HTML tags like
incorrectly

Leaving no space causing words to stick together

In JSX, to add a space between elements or text, use curly braces with a string: {' '}. Plain quotes inside tags cause errors.

4fill in blank

hard

Fill both blanks to create a JSX expression that shows a list of items from an array.

React

const items = ['Apple', 'Banana', 'Cherry'];
const list = <ul>[1].map((item) => <li key={item}>[2]</li>)</ul>;

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

Aitems

Bitem

Cfruits

Dfruit

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names like 'fruits' or 'fruit'

Not using map to loop over the array

Forgetting to use key attribute in list items

We use items.map to loop over the array and item to show each fruit inside list items.

5fill in blank

hard

Fill all three blanks to create a React component that uses JSX to display a greeting with a name prop.

React

function Greeting([1]) {
  return <h1>Hello, [2]!</h1>;
}

const element = <Greeting [3]="Alice" />;

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

Aname

Duser

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for the prop in different places

Forgetting to destructure props in the function parameter

Passing props with wrong attribute names

The component receives a prop called name. We use it inside JSX and pass it as an attribute when using the component.

Practice

1. What is JSX in React?

easy

A. A syntax that lets you write HTML-like code inside JavaScript

B. A CSS framework for styling React components

C. A database query language used with React

D. A tool to compile JavaScript into machine code

Solution

1. Step 1: Understand JSX purpose

   JSX allows writing HTML-like tags directly in JavaScript code, making UI code easier to write and read.

2. Step 2: Identify incorrect options

   Options B, C, and D describe unrelated tools or concepts not connected to JSX.

3. Final Answer:

   A syntax that lets you write HTML-like code inside JavaScript -> Option A

4. Quick Check:

   JSX = HTML-like code in JavaScript [OK]

Hint: JSX looks like HTML but is inside JavaScript code [OK]

Common Mistakes:

• Confusing JSX with CSS or styling tools
• Thinking JSX is a separate language
• Believing JSX is a database query language

2. Which of the following is the correct way to write a JSX element?

easy

A. <div>Hello World

B. div>Hello World

C. Hello World

D. {div}Hello World{/div}

Solution

1. Step 1: Check JSX tag syntax

   JSX elements must have opening and closing tags properly enclosed in angle brackets, like <div>Hello World</div>.

2. Step 2: Identify syntax errors in other options

   div>Hello World</div> misses the opening angle bracket, C misses the closing tag, and D uses curly braces incorrectly.

3. Final Answer:

   <div>Hello World</div> -> Option C

4. Quick Check:

   Proper JSX tags use <tag>content</tag> [OK]

Hint: JSX tags look like HTML tags with < and > [OK]

Common Mistakes:

• Omitting angle brackets around tags
• Forgetting closing tags
• Using curly braces instead of angle brackets for tags

3. What will this JSX code render?

const element = <h1>Hello, {"React"} & JSX!</h1>;
ReactDOM.render(element, document.getElementById('root'));

medium

A. Hello, {"React"} & JSX!

B. SyntaxError due to curly braces

C. Hello, React & JSX!

D. Hello, React & JSX!

Solution

1. Step 1: Understand JSX expression inside curly braces

   The string "React" inside curly braces is evaluated and inserted as text inside the h1 element.

2. Step 2: Recognize HTML entities and output

   The & symbol renders as & in the browser, so the final rendered text is Hello, React & JSX! inside an h1 tag.

3. Final Answer:

   <h1>Hello, React & JSX!</h1> -> Option D

4. Quick Check:

   JSX expressions render evaluated content [OK]

Hint: Curly braces insert JavaScript values inside JSX [OK]

Common Mistakes:

• Thinking curly braces print raw code
• Confusing HTML entities with literal text
• Expecting syntax error from curly braces

4. Identify the error in this JSX code:

const element = <div>Hello {name}</div>
ReactDOM.render(element, document.getElementById('root'));

Assuming name is not defined anywhere.

medium

A. ReferenceError because 'name' is not defined

B. SyntaxError due to missing quotes around name

C. Renders 'Hello name' as plain text

D. No error, renders empty space after Hello

Solution

1. Step 1: Check variable usage inside JSX

   JSX expressions inside curly braces expect valid JavaScript variables or expressions. Here, 'name' is not defined.

2. Step 2: Understand runtime behavior

   Using an undefined variable causes a ReferenceError at runtime, stopping rendering.

3. Final Answer:

   ReferenceError because 'name' is not defined -> Option A

4. Quick Check:

   Undefined variables in JSX cause ReferenceError [OK]

Hint: Variables in JSX must be defined before use [OK]

Common Mistakes:

• Assuming missing quotes cause syntax error
• Thinking JSX prints variable names as text
• Believing undefined variables render empty strings

5. How can you include a JavaScript expression inside JSX to display the sum of 2 + 3?

hard

A. The sum is {"2 + 3"}

B. The sum is {2 + 3}

C. The sum is (2 + 3)

D. The sum is "2 + 3"

Solution

1. Step 1: Use curly braces for JavaScript expressions in JSX

   JSX lets you insert JavaScript expressions inside curly braces to evaluate and display their result.

2. Step 2: Evaluate each option's expression

   The sum is {2 + 3}

   correctly uses curly braces with 2 + 3, which evaluates to 5. Options A and B treat it as a string, and C uses parentheses without curly braces, so it won't evaluate.

3. Final Answer:

   <p>The sum is {2 + 3}</p> -> Option B

4. Quick Check:

   Curly braces evaluate JS expressions inside JSX [OK]

Hint: Use curly braces to evaluate expressions inside JSX [OK]

Common Mistakes:

• Putting expressions inside quotes disables evaluation
• Using parentheses without curly braces
• Confusing strings with expressions