JSX vs HTML differences in React - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to use the correct JSX attribute for CSS classes.

React

<div [1]="container">Hello World</div>

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

Aid

Bclass

Cstyle

DclassName

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'class' instead of 'className' causes errors in JSX.

In JSX, className is used instead of class to assign CSS classes.

2fill in blank

medium

Complete the code to correctly write a self-closing tag in JSX.

React

<img src="logo.png" [1]>

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

A/>

B</img>

C>

D></img>

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the slash in self-closing tags causes syntax errors.

In JSX, self-closing tags must end with /> to be valid.

3fill in blank

hard

Fix the error in the JSX code by choosing the correct attribute for inline styles.

React

<div [1]={{ color: 'red' }}>Text</div>

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

AclassName

Bstyle

CstyleName

Dcss

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'className' or 'styleName' instead of 'style' for inline styles.

In JSX, the style attribute accepts a JavaScript object for inline styles.

4fill in blank

hard

Fill both blanks to correctly write a JSX event handler for a button click.

React

<button [1]=[2]>Click me</button>

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

AonClick

Bonclick

C{handleClick}

DhandleClick

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase event names like 'onclick'.

Wrapping the handler in extra braces inside the attribute.

JSX uses camelCase event names like onClick. The handler is passed as a JavaScript expression without braces inside the attribute value.

5fill in blank

hard

Fill all three blanks to correctly write a JSX fragment with two paragraphs.

React

<>[1][2][3]<p>Second paragraph</p></>

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

A<p>First paragraph</p>

BFirst paragraph

C</p>

D<p>

Attempts:

3 left

💡 Hint

Common Mistakes

Putting raw text outside paragraph tags.

Not closing paragraph tags properly.

JSX fragments allow grouping without extra nodes. Paragraph tags must open and close properly around text.

Practice

1. Which attribute should you use in JSX to add CSS classes to an element?

easy

A. cssClass

B. class

C. className

D. styleClass

Solution

1. Step 1: Recall JSX attribute rules

   In JSX, the HTML attribute class is replaced by className because class is a reserved word in JavaScript.

2. Step 2: Identify correct attribute for CSS classes

   Therefore, to add CSS classes in JSX, you must use className.

3. Final Answer:

   className -> Option C

4. Quick Check:

   JSX uses className, not class [OK]

Hint: Remember: JSX uses className, not class for CSS classes [OK]

Common Mistakes:

• Using 'class' instead of 'className' causes errors
• Confusing 'className' with 'cssClass'
• Trying to use 'styleClass' which doesn't exist

2. Which of the following is the correct way to write a label with a 'for' attribute in JSX?

easy

A. Name

B. Name

C. Name

D. Name

Solution

1. Step 1: Understand JSX attribute naming

   In JSX, the HTML attribute for is replaced by htmlFor because for is a reserved word in JavaScript.

2. Step 2: Check correct casing and spelling

   The correct attribute is htmlFor with capital F, so <label htmlFor="inputId">Name</label> is correct.

3. Final Answer:

   <label htmlFor="inputId">Name</label> -> Option A

4. Quick Check:

   Use htmlFor, not for in JSX labels [OK]

Hint: Use htmlFor (camelCase) instead of for in JSX labels [OK]

Common Mistakes:

• Using 'for' attribute directly causes syntax errors
• Writing 'htmlfor' with lowercase f is incorrect
• Using non-existent attributes like 'forId'

3. What will be the rendered output of this JSX code?

const element = <input type="checkbox" checked="true" />;
ReactDOM.render(element, document.getElementById('root'));

medium

A. A checkbox input with checked attribute as string

B. A checked checkbox input

C. Syntax error due to checked attribute value

D. An unchecked checkbox input

Solution

1. Step 1: Analyze checked attribute in JSX

   In JSX, checked="true" without curly braces sets the prop to the string "true".

2. Step 2: Understand rendering of boolean attributes

   React renders <input type="checkbox" checked="true" />. Browsers treat the presence of the checked attribute (any non-empty value) as checked for uncontrolled checkboxes.

3. Final Answer:

   A checked checkbox input -> Option B

4. Quick Check:

   Attribute presence checks uncontrolled checkbox [OK]

Hint: checked="true" renders checked checkbox (attribute presence) [OK]

Common Mistakes:

• Thinking checked="true" leaves checkbox unchecked
• Expecting string value to cause syntax error
• Confusing uncontrolled render with controlled components

4. Identify the error in this JSX snippet:

const element = <div class="container">Hello</div>;

medium

A. Using class instead of className

B. Using double quotes instead of single quotes

C. Missing closing tag for div

D. Using semicolon inside JSX

Solution

1. Step 1: Check attribute names in JSX

   JSX does not use the HTML attribute class. Instead, it uses className because class is a reserved word in JavaScript.

2. Step 2: Verify other parts of the snippet

   The quotes and closing tag are correct. The semicolon is outside JSX and valid in JavaScript.

3. Final Answer:

   Using class instead of className -> Option A

4. Quick Check:

   JSX requires className, not class [OK]

Hint: Replace class with className in JSX attributes [OK]

Common Mistakes:

• Using class attribute causes React warnings or errors
• Thinking quotes style causes errors
• Confusing semicolon placement inside JSX

5. You want to apply inline styles to a JSX element to make text red and bold. Which is the correct way?

hard

A. Text

B. Text

C. Text

D. Text

Solution

1. Step 1: Understand JSX style attribute syntax

   In JSX, the style attribute expects a JavaScript object, so you use double curly braces: the outer for embedding JS, the inner for the object.

2. Step 2: Check property names and values

   CSS properties use camelCase in JSX, so fontWeight is correct. Values are strings like 'red' and 'bold'.

3. Final Answer:

   <div style={{color: 'red', fontWeight: 'bold'}}>Text</div> -> Option D

4. Quick Check:

   Use double braces and camelCase for inline styles [OK]

Hint: Use double braces and camelCase keys for JSX inline styles [OK]

Common Mistakes:

• Using string style attribute instead of object
• Missing curly braces around style object
• Using CSS property names with hyphens instead of camelCase