Embedding expressions in JSX in React - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this React component?

Consider the following React component. What will it render inside the <div>?

React

import React from 'react';

function Greeting() {
  const name = 'Alice';
  const age = 25;
  return <div>Hello, {name}! You are {age} years old.</div>;
}

export default Greeting;

A Hello, {name}! You are {age} years old.

B Hello, Alice! You are 25 years old.

C Hello, Alice! You are {age} years old.

D Hello, {name}! You are 25 years old.

💡 Hint

Remember that expressions inside curly braces in JSX are evaluated and replaced with their values.

In JSX, expressions inside curly braces are evaluated. So {name} becomes 'Alice' and {age} becomes 25, producing the full string.

📝 Syntax

intermediate

Which JSX expression is valid to embed a JavaScript expression?

Which of the following JSX snippets correctly embeds a JavaScript expression to show the sum of 2 + 3?

A <div>{2 + '3'}</div>

B <div>2 + 3</div>

C <div>{'2 + 3'}</div>

D <div>{2 + 3}</div>

💡 Hint

JSX expressions inside curly braces are evaluated as JavaScript.

Option D evaluates 2 + 3 to 5 and renders it. Option D renders the string '2 + 3'. Option D renders the string '2 + 3'. Option D concatenates number 2 and string '3' to '23'.

❓ state_output

advanced

What will be displayed after clicking the button once?

Given this React component, what text will appear inside the <div> after clicking the button once?

React

import React, { useState } from 'react';

function Counter() {
  const [count, setCount] = useState(0);
  return (
    <>
      <div>Count: {count}</div>
      <button onClick={() => setCount(count + 1)}>Increment</button>
    </>
  );
}

export default Counter;

A Count: 1

B Count: 0

C Count: undefined

D Count: NaN

💡 Hint

Clicking the button calls setCount with count + 1, updating the state.

Initially count is 0. Clicking the button increases count to 1, so the div shows 'Count: 1'.

🔧 Debug

advanced

Why does this JSX code cause an error?

Examine this JSX snippet. Why does it cause a syntax error?

React

const element = <div>{if (true) { 'Yes' } else { 'No' }}</div>;

A JSX expressions cannot contain statements like if; only expressions are allowed.

B The curly braces are missing around the if statement.

C The strings 'Yes' and 'No' must be wrapped in parentheses.

D JSX requires a semicolon after the if statement inside curly braces.

💡 Hint

JSX expressions expect a single JavaScript expression, not statements.

The if statement is a JavaScript statement, not an expression. JSX curly braces only accept expressions like ternary operators.

🧠 Conceptual

expert

What is the value of 'result' after rendering this React component?

Consider this React component. What is the value of the variable 'result' after the component renders?

React

import React from 'react';

function Example() {
  const a = 5;
  const b = 10;
  const result = <>{a > b ? 'Greater' : a < b ? 'Smaller' : 'Equal'}</>;
  return <div>{result}</div>;
}

export default Example;

A Greater

B Equal

C Smaller

D undefined

💡 Hint

The expression uses nested ternary operators to compare a and b.

Since 5 is less than 10, the expression evaluates to 'Smaller'.

Practice

1. In React JSX, how do you embed a JavaScript variable name inside a <p> tag to display it?

easy

A. name

B. {name}

C. ${name}

D. \{name\}

Solution

1. Step 1: Understand JSX embedding syntax

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

2. Step 2: Apply embedding to variable

   To display the variable name, write it inside curly braces within the JSX tag: {name}.

3. Final Answer:

   <p>{name}</p> -> Option B

4. Quick Check:

   Use curly braces {} to embed variables [OK]

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

Common Mistakes:

• Using quotes instead of curly braces
• Trying to use template literals inside JSX directly
• Escaping curly braces incorrectly

2. Which of the following is the correct way to embed a JavaScript expression that adds two numbers inside JSX?

easy

A. {2 + 3}

B. 2 + 3

C. ${2 + 3}

D. {'2 + 3'}

Solution

1. Step 1: Recognize expression embedding

   JSX requires expressions inside curly braces to evaluate them, so {2 + 3} will calculate the sum.

2. Step 2: Identify correct syntax

   {2 + 3} correctly uses curly braces with the expression 2 + 3. Other options treat it as plain text or incorrect syntax.

3. Final Answer:

   <div>{2 + 3}</div> -> Option A

4. Quick Check:

   Curly braces evaluate expressions in JSX [OK]

Hint: Wrap expressions in {} to evaluate inside JSX [OK]

Common Mistakes:

• Putting expressions as plain text without braces
• Using template literals without braces
• Wrapping expressions in quotes

3. What will be rendered by this React component?

function Greeting() {
  const hour = 10;
  return <h1>Good {hour < 12 ? 'Morning' : 'Evening'}!</h1>;
}

medium

A. Good {hour < 12 ? 'Morning' : 'Evening'}!

B. Good Evening!

C. SyntaxError

D. Good Morning!

Solution

1. Step 1: Evaluate the conditional expression

   The variable hour is 10, which is less than 12, so the condition hour < 12 is true.

2. Step 2: Determine the rendered string

   Because the condition is true, the expression returns 'Morning', so the rendered output is <h1>Good Morning!</h1>.

3. Final Answer:

   <h1>Good Morning!</h1> -> Option D

4. Quick Check:

   Conditional expression inside {} renders correct text [OK]

Hint: Evaluate expressions inside {} before rendering [OK]

Common Mistakes:

• Thinking JSX shows raw expressions
• Confusing true/false in ternary
• Missing curly braces for expressions

4. Identify the error in this JSX snippet:

const count = 5;
return <div>You have {count} new messages</div>;

medium

A. No error, code is correct

B. Missing curly braces around count

C. JSX must use parentheses around return value

D. Curly braces should be escaped

Solution

1. Step 1: Check expression embedding

   The variable count is correctly embedded inside curly braces {count} within JSX.

2. Step 2: Verify JSX syntax

   The JSX syntax is valid; parentheses around return are optional for single-line JSX.

3. Final Answer:

   No error, code is correct -> Option A

4. Quick Check:

   Curly braces correctly embed variables in JSX [OK]

Hint: Curly braces embed variables; parentheses optional for single JSX line [OK]

Common Mistakes:

• Thinking parentheses are mandatory for return
• Trying to escape curly braces unnecessarily
• Omitting curly braces around variables

5. Given this React component, what will be the output?

function ListItems() {
  const items = ['Apple', 'Banana', 'Cherry'];
  return (
    <ul>
      {items.map(item => <li key={item}>{item.length > 5 ? item : 'Short'}</li>)}
    </ul>
  );
}

hard

A. ShortShortShort

B. AppleBananaCherry

C. ShortBananaCherry

D. Runtime error due to missing keys

Solution

1. Step 1: Evaluate each item length

   Items are 'Apple'(5), 'Banana'(6), 'Cherry'(6). The condition item.length > 5 is true for 'Banana' and 'Cherry', false for 'Apple'.

2. Step 2: Apply conditional rendering

   For 'Apple', length is 5 (not > 5), so it renders 'Short'. For 'Banana' and 'Cherry', it renders the item name.

3. Step 3: Check keys and JSX structure

   Each <li> has a unique key from the item string, so no error occurs.

4. Final Answer:

   <ul><li>Short</li><li>Banana</li><li>Cherry</li></ul> -> Option C

5. Quick Check:

   Conditional expression inside map renders correct list [OK]

Hint: Check condition inside map for each item before rendering [OK]

Common Mistakes:

• Assuming all items render their names
• Forgetting to add keys in list items
• Confusing length comparison operator