If–else statement in Javascript - Mini Project: Build & Apply

If-else statement

📖 Scenario: You are helping a small shop decide if a customer gets a discount based on their purchase amount.

🎯 Goal: Build a simple program that checks if the purchase amount is enough for a discount and shows the correct message.

📋 What You'll Learn

Create a variable to store the purchase amount.

Create a variable to store the discount threshold.

Use an if-else statement to check if the purchase amount is greater than or equal to the discount threshold.

Print a message showing if the customer gets a discount or not.

💡 Why This Matters

🌍 Real World

Stores often give discounts based on how much customers buy. This helps encourage bigger purchases.

💼 Career

Understanding if-else statements is important for making decisions in programs, like showing messages or calculating prices.

1

Create the purchase amount variable

Create a variable called purchaseAmount and set it to 120.

Javascript

// Your code here

Hint

Use let to create the variable and assign the number 120.

2

Create the discount threshold variable

Create a variable called discountThreshold and set it to 100.

Javascript

let purchaseAmount = 120;
// Your code here

Hint

Use let to create the variable and assign the number 100.

3

Write the if-else statement

Write an if statement that checks if purchaseAmount is greater than or equal to discountThreshold. Inside the if, create a variable called message and set it to "You get a discount!". In the else part, set message to "No discount this time.".

Javascript

let purchaseAmount = 120;
let discountThreshold = 100;
// Your code here

Hint

Use if (purchaseAmount >= discountThreshold) to check the condition. Then assign the correct message inside each block.

4

Print the message

Write console.log(message) to print the message to the console.

Javascript

let purchaseAmount = 120;
let discountThreshold = 100;
let message;
if (purchaseAmount >= discountThreshold) {
    message = "You get a discount!";
} else {
    message = "No discount this time.";
}
// Your code here

Hint

Use console.log(message) to show the message in the console.

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