If–else statement in Javascript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of nested if–else

What is the output of the following JavaScript code?

Javascript

let x = 10;
if (x > 5) {
  if (x < 15) {
    console.log('A');
  } else {
    console.log('B');
  }
} else {
  console.log('C');
}

A B

B C

C A

D undefined

💡 Hint

Check the conditions step by step.

x is 10, which is greater than 5 and less than 15, so the first if and the nested if both run, printing 'A'.

❓ Predict Output

intermediate

If–else with logical operators

What will this code print to the console?

Javascript

let a = 3;
let b = 7;
if (a > 5 && b < 10) {
  console.log('X');
} else {
  console.log('Y');
}

A X

B Y

C undefined

D SyntaxError

💡 Hint

Remember how && works: both conditions must be true.

a > 5 is false (3 > 5 is false), so the whole condition is false, so else runs printing 'Y'.

❓ Predict Output

advanced

If–else with else if branches

What is the output of this code snippet?

Javascript

let score = 75;
if (score >= 90) {
  console.log('A');
} else if (score >= 80) {
  console.log('B');
} else if (score >= 70) {
  console.log('C');
} else {
  console.log('F');
}

A C

B A

C B

D F

💡 Hint

Check each condition in order.

75 is not >= 90 or 80 but is >= 70, so it prints 'C'.

❓ Predict Output

advanced

If–else with variable reassignment

What is the value of variable result after running this code?

Javascript

let num = 0;
let result;
if (num) {
  result = 'Truthy';
} else {
  result = 'Falsy';
}

A 'Falsy'

B undefined

C 'Truthy'

D ReferenceError

💡 Hint

Remember how JavaScript treats 0 in conditions.

0 is falsy in JavaScript, so else branch runs setting result to 'Falsy'.

❓ Predict Output

expert

If–else with complex condition and side effects

What will be printed by this code?

Javascript

let x = 5;
if ((x += 3) > 7) {
  console.log(x);
} else {
  console.log(x - 1);
}

A 6

B 7

C 5

D 8

💡 Hint

The condition changes x before comparing.

x starts at 5, then x += 3 makes x 8, which is > 7, so it prints 8.

Practice

1. What does an if-else statement do in JavaScript?

easy

A. It repeats a block of code multiple times.

B. It creates a new variable.

C. It defines a function to be used later.

D. It chooses between two actions based on a condition.

Solution

1. Step 1: Understand the purpose of if-else

   An if-else statement lets the program decide between two paths depending on a condition.

2. Step 2: Match the description to the options

   Only It chooses between two actions based on a condition. describes choosing between two actions based on a condition.

3. Final Answer:

   It chooses between two actions based on a condition. -> Option D

4. Quick Check:

   If-else = choose between two actions [OK]

Hint: If-else picks one of two paths based on true or false [OK]

Common Mistakes:

• Confusing if-else with loops
• Thinking if-else defines functions
• Believing if-else creates variables

2. Which of the following is the correct syntax for an if-else statement in JavaScript?

easy

A. if (condition) { } else { }

B. if condition { } else { }

C. if (condition) then { } else { }

D. if condition then { } else { }

Solution

1. Step 1: Recall JavaScript if-else syntax

   JavaScript requires parentheses around the condition and braces for blocks: if (condition) { } else { }

2. Step 2: Compare options to correct syntax

   Only if (condition) { } else { } uses parentheses and braces correctly without extra keywords.

3. Final Answer:

   if (condition) { } else { } -> Option A

4. Quick Check:

   Correct syntax uses parentheses and braces [OK]

Hint: Remember: condition in ( ), blocks in { } [OK]

Common Mistakes:

• Omitting parentheses around condition
• Adding 'then' keyword (not in JS)
• Missing braces for code blocks

3. What will be the output of this code?

let age = 18;
if (age >= 18) {
  console.log('Adult');
} else {
  console.log('Minor');
}

medium

A. Adult

B. Minor

C. undefined

D. Error

Solution

1. Step 1: Evaluate the condition age >= 18

   Since age is 18, the condition age >= 18 is true.

2. Step 2: Determine which block runs

   The if block runs and prints 'Adult'. The else block is skipped.

3. Final Answer:

   Adult -> Option A

4. Quick Check:

   Condition true -> if block runs -> 'Adult' [OK]

Hint: Check if condition is true or false to pick output [OK]

Common Mistakes:

• Thinking 18 is less than 18
• Confusing else block runs when condition is true
• Expecting syntax error

4. Find the error in this code:

let score = 75;
if score >= 60 {
  console.log('Pass');
} else {
  console.log('Fail');
}

medium

A. Using else without if

B. Missing semicolon after console.log

C. Missing parentheses around the condition

D. Variable score is not declared

Solution

1. Step 1: Check if-else syntax

   JavaScript requires parentheses around the condition in if statements.

2. Step 2: Identify the missing parentheses

   The code has if score >= 60 { ... } but it should be if (score >= 60) { ... }

3. Final Answer:

   Missing parentheses around the condition -> Option C

4. Quick Check:

   if condition must be in ( ) [OK]

Hint: Always put condition inside ( ) after if [OK]

Common Mistakes:

• Forgetting parentheses around condition
• Thinking semicolon is required after console.log block
• Confusing else usage

5. You want to print 'Even' if a number is even, and 'Odd' if it is odd. Which code correctly uses if-else to do this?

let num = 7;
// Choose the correct code snippet

hard

A. if (num % 2 != 0) {
console.log('Even');
} else {
console.log('Odd');
}

B. if (num % 2 === 0) {
console.log('Even');
} else {
console.log('Odd');
}

C. if (num % 2) {
console.log('Even');
} else {
console.log('Odd');
}

D. if (num / 2 === 0) {
console.log('Even');
} else {
console.log('Odd');
}

Solution

1. Step 1: Understand how to check even numbers

   A number is even if remainder when divided by 2 is zero: num % 2 === 0.

2. Step 2: Check each option's condition

   if (num % 2 === 0) { console.log('Even'); } else { console.log('Odd'); } correctly checks num % 2 === 0. Others either use wrong operator or logic.

3. Final Answer:

   if (num % 2 === 0) { console.log('Even'); } else { console.log('Odd'); } -> Option B

4. Quick Check:

   Even check uses num % 2 === 0 [OK]

Hint: Use modulo (%) to test evenness: zero remainder means even [OK]

Common Mistakes:

• Using division (/) instead of modulo (%)
• Checking if remainder is truthy instead of zero
• Reversing even and odd conditions