JSX syntax rules in React - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to correctly render a JSX element.

React

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

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

A class="greeting"

B className="greeting"

C classname="greeting"

D className=greeting

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'class' instead of 'className'

Not quoting the attribute value

Using lowercase 'classname'

In JSX, the correct way to add a CSS class is using className with quotes around the value.

2fill in blank

medium

Complete the code to correctly embed a JavaScript expression inside JSX.

React

const name = "Alice";
const element = <h1>Hello, [1]!</h1>;

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

A{name}

B[name]

Cname

D"name"

Attempts:

3 left

💡 Hint

Common Mistakes

Using the variable name without braces

Using quotes around the variable name

Using array brackets

In JSX, JavaScript expressions must be wrapped in curly braces {} to be evaluated.

3fill in blank

hard

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

React

const element = <input type="checkbox" [1] />;

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

Achecked="true"

Bchecked

Cchecked={true}

Dchecked=true

Attempts:

3 left

💡 Hint

Common Mistakes

Using just the attribute name without value

Using quotes around true

Assigning true without braces

In JSX, boolean attributes must be set using curly braces with a boolean value, like checked={true}.

4fill in blank

hard

Fill both blanks to correctly write a JSX fragment with two elements.

React

return (
  <>
    <h1[1]>Title</h1>
    <p[2]>Paragraph</p>
  </>
);

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

A className="header"

B class="header"

C className="text"

D class="text"

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'class' instead of 'className'

Not quoting attribute values

Use className with quotes for both elements to add CSS classes in JSX.

5fill in blank

hard

Fill all three blanks to create a JSX element with a dynamic style and event handler.

React

const buttonStyle = { color: 'blue' };

return (
  <button style=[1] onClick=[2] disabled=[3]>
    Click me
  </button>
);

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

AbuttonStyle

B() => alert('Clicked!')

Cfalse

DbuttonStyle.color

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a string instead of a function to onClick

Passing a string instead of a boolean to disabled

Passing a property instead of the whole style object

Use the buttonStyle object for style, a function for onClick, and a boolean for disabled.

Practice

1. Which of the following is correct JSX syntax for embedding a JavaScript expression inside HTML?

easy

A. <h1>Hello, {name}!</h1>

B. <h1>Hello, (name)!</h1>

C. <h1>Hello, $name!</h1>

D. <h1>Hello, &{name}!</h1>

Solution

1. Step 1: Understand JSX expression embedding

   JSX uses curly braces {} to embed JavaScript expressions inside HTML-like code.

2. Step 2: Check each option for correct syntax

   <h1>Hello, {name}!</h1> correctly uses curly braces around the variable name. The other options use invalid syntax for embedding expressions.

3. Final Answer:

   <h1>Hello, {name}!</h1> -> Option A

4. Quick Check:

   Curly braces for JS expressions = <h1>Hello, {name}!</h1> [OK]

Hint: Use curly braces {} to embed JavaScript in JSX [OK]

Common Mistakes:

• Using parentheses () instead of curly braces
• Using $ sign like template strings inside JSX
• Adding extra symbols like & before curly braces

2. Which JSX snippet is syntactically correct?

easy

A. <p>Hello<p>

B. <div><img src='logo.png'></div>

C. <input type='text' />

D. <br>

Solution

1. Step 1: Check self-closing tags in JSX

   In JSX, tags like input, img, and br must be self-closed with a slash /.

2. Step 2: Validate each option

   <input type='text' /> correctly self-closes input. <div><img src='logo.png'></div> misses self-closing on img. <p>Hello<p> has an unclosed p tag. <br> misses self-closing on br.

3. Final Answer:

   <input type='text' /> -> Option C

4. Quick Check:

   Self-close void tags with / = <input type='text' /> [OK]

Hint: Always self-close void tags like in JSX [OK]

Common Mistakes:

• Forgetting the slash on self-closing tags
• Leaving tags unclosed
• Using HTML void tags without self-closing

3. What will this JSX code render?

const name = 'Alice';
const element = <div>Hello, {name.toUpperCase()}!</div>;

medium

A. <div>Hello, Alice!</div>

B. <div>Hello, ALICE!</div>

C. <div>Hello, {name.toUpperCase()}!</div>

D. SyntaxError

Solution

1. Step 1: Evaluate the JavaScript expression inside JSX

   The expression {name.toUpperCase()} calls the toUpperCase() method on the string 'Alice', resulting in 'ALICE'.

2. Step 2: Understand JSX rendering

   JSX replaces the expression with its evaluated result, so the rendered output is <div>Hello, ALICE!</div>.

3. Final Answer:

   <div>Hello, ALICE!</div> -> Option B

4. Quick Check:

   JS expression evaluated = <div>Hello, ALICE!</div> [OK]

Hint: JSX renders evaluated expressions, not raw code [OK]

Common Mistakes:

• Expecting JSX to show raw JavaScript code
• Confusing string methods inside JSX
• Thinking JSX does not evaluate expressions

4. Identify the error in this JSX code:

const element = <div>
  <p>Welcome</p>
  <p>User</p>
</div>;

const wrongElement = <p>Hello</p>
<p>World</p>;

medium

A. JSX expressions cannot contain multiple <p> tags

B. JSX requires all tags to be self-closing

C. JSX does not allow text inside <p> tags

D. JSX must have only one parent element per block

Solution

1. Step 1: Analyze the JSX structure

   The first element uses a single parent div wrapping two p tags, which is correct. The second snippet has two sibling p tags without a parent wrapper.

2. Step 2: Recall JSX rules about parent elements

   JSX requires one parent element per block. Multiple sibling elements must be wrapped in a single parent or a fragment.

3. Final Answer:

   JSX must have only one parent element per block -> Option D

4. Quick Check:

   One parent element rule = JSX must have only one parent element per block [OK]

Hint: Wrap multiple JSX elements in one parent tag [OK]

Common Mistakes:

• Leaving sibling JSX elements unwrapped
• Thinking multiple root elements are allowed
• Confusing self-closing tags with parent wrapping

5. You want to render a list of names inside a JSX component. Which snippet correctly uses JSX syntax to do this?

const names = ['Anna', 'Bob', 'Cara'];

A) <ul>{names.map(name => <li>{name}</li>)}</ul>

B) <ul>{names.forEach(name => <li>{name}</li>)}</ul>

C) <ul>{names.map(name => <li>name</li>)}</ul>

D) <ul>{names.map(name => <li>{name.toUpperCase()}</li>)}</ul>

hard

A. Correctly maps names to list items with JSX expressions

B. Uses forEach which returns undefined, so no list items render

C. Does not embed the variable, so 'name' is rendered literally

D. Maps names but transforms them to uppercase before rendering

Solution

1. Step 1: Understand how to render lists in JSX

   Use map to transform array items into JSX elements. Each item must be embedded inside curly braces.

2. Step 2: Evaluate each option

   The snippet {names.map(name => <li>{name}</li>)} correctly uses map and embeds {name}. The forEach snippet returns undefined, so no list items render. The snippet <li>name</li> renders the literal string 'name' because it lacks curly braces. The toUpperCase() snippet uses valid JSX syntax but transforms names to uppercase, which is not the original list.

3. Final Answer:

   Correctly maps names to list items with JSX expressions -> Option A

4. Quick Check:

   Use map with curly braces for list rendering = Correctly maps names to list items with JSX expressions [OK]

Hint: Use map with curly braces to render lists in JSX [OK]

Common Mistakes:

• Using forEach instead of map for rendering
• Forgetting curly braces around variables
• Rendering variable names as plain text