If–else statement in Javascript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if a number is positive.

Javascript

if (num [1] 0) {
  console.log('Positive');
} else {
  console.log('Not positive');
}

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

A===

B!==

C<

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '===' instead of '>' will only check if num equals zero.

Using '<' will check if the number is negative, not positive.

The condition 'num > 0' checks if the number is greater than zero, meaning it is positive.

2fill in blank

medium

Complete the code to print 'Even' if the number is even.

Javascript

if (num % 2 [1] 0) {
  console.log('Even');
} else {
  console.log('Odd');
}

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

A!==

B>

C===

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!== 0' will check for odd numbers instead of even.

Using '>' or '<' does not correctly check for evenness.

The condition 'num % 2 === 0' checks if the remainder when dividing by 2 is zero, meaning the number is even.

3fill in blank

hard

Fix the error in the if condition to check if age is at least 18.

Javascript

if (age [1] 18) {
  console.log('Adult');
} else {
  console.log('Minor');
}

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

A>=

B<=

C<

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' or '<=' checks for younger ages, not adults.

Using '==' only checks if age equals 18 exactly.

The condition 'age >= 18' checks if age is 18 or older, meaning adult.

4fill in blank

hard

Fill both blanks to check if a number is between 10 and 20 (inclusive).

Javascript

if (num [1] 10 && num [2] 20) {
  console.log('Between 10 and 20');
} else {
  console.log('Outside range');
}

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

A>=

B<

C<=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' or '<' alone excludes the boundary numbers 10 or 20.

Mixing up the operators order can cause wrong logic.

The condition 'num >= 10 && num <= 20' checks if num is between 10 and 20 including both ends.

5fill in blank

hard

Fill both blanks to create an if-else that prints 'Child', 'Teen', or 'Adult' based on age.

Javascript

if (age [1] 12) {
  console.log('Child');
} else if (age [2] 19) {
  console.log('Teen');
} else {
  console.log('Adult');
}

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

A<=

B<

C>=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>=' in the first condition would reverse logic.

Using '>' in the else if condition would cause wrong grouping.

The code checks if age is less than or equal to 12 for 'Child', less than 19 for 'Teen', else 'Adult'.

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