JSX vs HTML differences in React

Introduction

JSX looks like HTML but is used in React to describe UI. It lets you write UI code inside JavaScript easily.

When building React components to create interactive web pages.

When you want to mix JavaScript logic with UI structure.

When you need to use dynamic data inside your UI elements.

When you want to write cleaner and more readable UI code in React.

Syntax

React

const element = <div className="container">Hello, world!</div>;

JSX uses className instead of class because class is a reserved word in JavaScript.

JSX expressions must have one parent element wrapping all content.

Examples

JSX uses checked as a boolean attribute with curly braces for JavaScript values.

React

<input type="checkbox" checked={true} />

JSX uses htmlFor instead of for to avoid conflict with JavaScript reserved words.

React

<label htmlFor="name">Name:</label>

JSX styles are written as JavaScript objects inside double curly braces.

React

<div style={{ color: 'red', fontSize: '16px' }}>Red Text</div>

Sample Program

This React component shows JSX differences: className for CSS class, htmlFor for label, boolean attribute checked, and inline styles as an object.

React

import React from 'react';

function Sample() {
  return (
    <div className="box" style={{ backgroundColor: 'lightblue', padding: '1rem' }}>
      <label htmlFor="title">Welcome!</label>
      <input type="checkbox" checked={true} />
      <p>This is JSX, not plain HTML.</p>
    </div>
  );
}

export default Sample;

Important Notes

JSX is not a string or HTML but a syntax that compiles to JavaScript calls.

Always use camelCase for event handlers like onClick in JSX.

Summary

JSX looks like HTML but uses JavaScript rules.

Use className instead of class, and htmlFor instead of for.

Attributes like styles and booleans use JavaScript syntax inside JSX.

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