If–else statement in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of an if–else statement in JavaScript?

An if–else statement lets the program choose between two paths: one if a condition is true, and another if it is false.

beginner

Write the basic syntax of an if–else statement in JavaScript.

if (condition) {
// code runs if condition is true
} else {
// code runs if condition is false
}

beginner

What happens if the condition in an if statement is false and there is no else block?

The code inside the if block is skipped, and the program continues after the if statement without running any alternative code.

intermediate

Can you use multiple else if blocks in JavaScript? What is their purpose?

Yes, multiple else if blocks let you check several conditions in order, running the code for the first true condition.

beginner

Explain with an example how if–else helps in decision making in code.

Example:
if (temperature > 30) {
console.log('It is hot');
} else {
console.log('It is not hot');
}
This helps the program decide what message to show based on temperature.

What will the following code print?
if (5 > 10) { console.log('Yes'); } else { console.log('No'); }

A Yes

B Nothing

C No

D Error

Since 5 is not greater than 10, the else block runs and prints 'No'.

Which keyword is used to check an additional condition after an if statement?

A else if

B else

C elseif

D elif

JavaScript uses 'else if' (two words) to check another condition after if.

What happens if the condition in an if statement is true?

A Nothing happens

B The else block runs

C The program stops

D The code inside the if block runs

When the condition is true, the code inside the if block runs.

Can an if statement exist without an else block?

A No, else is required

B Yes, else is optional

C Only if the condition is true

D Only if the condition is false

The else block is optional; you can have just an if statement.

What is the output of this code?
if (false) { console.log('A'); } else if (true) { console.log('B'); } else { console.log('C'); }

A B

B No output

C C

D A

The first condition is false, the else if condition is true, so it prints 'B'.

Describe how an if–else statement controls the flow of a program.

Think about how the program chooses what code to run based on a question.

Write a simple if–else statement in JavaScript that checks if a number is positive or not.

Use console.log to show messages for both cases.

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