Comparison operators in Javascript - Mini Project: Build & Apply

Comparison Operators in JavaScript

📖 Scenario: You are creating a simple program to compare ages of two friends to see who is older or if they are the same age.

🎯 Goal: Build a JavaScript program that stores two ages, compares them using comparison operators, and prints the correct message about who is older or if they are the same age.

📋 What You'll Learn

Create two variables with exact names and values for ages

Create a variable to hold the age difference

Use comparison operators to check which age is greater or if they are equal

Print the correct message based on the comparison

💡 Why This Matters

🌍 Real World

Comparing values is common in apps like age verification, sorting lists, or decision making.

💼 Career

Understanding comparison operators and conditional logic is essential for any programming job.

1

Create age variables

Create two variables called ageAlice and ageBob with the exact values 25 and 30 respectively.

Javascript

// Create variables ageAlice and ageBob with values 25 and 30
// Your code here

Hint

Use const to create variables and assign the numbers 25 and 30.

2

Calculate age difference

Create a variable called ageDifference that stores the result of ageBob - ageAlice.

Javascript

const ageAlice = 25;
const ageBob = 30;
// Create ageDifference as ageBob minus ageAlice
// Your code here

Hint

Subtract ageAlice from ageBob and store it in ageDifference.

3

Compare ages using comparison operators

Use if, else if, and else statements with comparison operators >, <, and === to check if ageAlice is greater than, less than, or equal to ageBob. Inside each block, assign a message string to a variable called result describing who is older or if they are the same age.

Javascript

const ageAlice = 25;
const ageBob = 30;
const ageDifference = ageBob - ageAlice;
// Use if, else if, else with comparison operators to set result message
// Your code here

Hint

Use if to check if Alice is older, else if to check if Bob is older, and else for when ages are equal.

4

Print the result

Write a console.log statement to print the value of the variable result.

Javascript

const ageAlice = 25;
const ageBob = 30;
const ageDifference = ageBob - ageAlice;
let result;
if (ageAlice > ageBob) {
    result = "Alice is older than Bob.";
} else if (ageAlice < ageBob) {
    result = "Bob is older than Alice.";
} else {
    result = "Alice and Bob are the same age.";
}
// Print the result variable
// Your code here

Hint

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

Practice

1. Which comparison operator checks if two values are equal in both value and type in JavaScript?

easy

A. !==

B. ==

C. !=

D. ===

Solution

1. Step 1: Understand equality operators

   == checks value equality but ignores type, while === checks both value and type.

2. Step 2: Identify strict equality operator

   === is the strict equality operator that compares both value and type.

3. Final Answer:

   === -> Option D

4. Quick Check:

   Strict equality = === [OK]

Hint: Use === to check value and type equality [OK]

Common Mistakes:

• Confusing == with ===
• Using != instead of !==
• Assuming == checks type

2. Which of the following is the correct syntax to check if variable a is NOT equal to variable b in both value and type?

easy

A. a !== b

B. a != b

C. a =! b

D. a !=== b

Solution

1. Step 1: Identify the strict inequality operator

   !== checks if two values are not equal in value or type.

2. Step 2: Check syntax correctness

   a !== b is correct syntax; others are either loose inequality or invalid.

3. Final Answer:

   a !== b -> Option A

4. Quick Check:

   Strict not equal = !== [OK]

Hint: Use !== for strict not equal check [OK]

Common Mistakes:

• Using != which ignores type
• Typing =! instead of !==
• Using too many equals signs

3. What will be the output of the following code?

console.log(5 == '5');
console.log(5 === '5');

medium

A. truetrue

B. truefalse

C. falsetrue

D. falsefalse

Solution

1. Step 1: Evaluate 5 == '5'

   Loose equality == converts types, so number 5 equals string '5', result is true.

2. Step 2: Evaluate 5 === '5'

   Strict equality === checks type too; number 5 is not string '5', result is false.

3. Final Answer:

   true
   false -> Option B

4. Quick Check:

   == true, === false [OK]

Hint: == compares value only; === compares value and type [OK]

Common Mistakes:

• Assuming both comparisons return true
• Confusing == and === behavior
• Ignoring type differences

4. Find the error in this code snippet:

if (a = 10) {
  console.log('Equal');
} else {
  console.log('Not equal');
}

medium

A. Variable a is not declared

B. Should use == instead of =

C. Should use === instead of =

D. No error, code is correct

Solution

1. Step 1: Identify assignment vs comparison

   = assigns value 10 to a, not compares it.

2. Step 2: Use strict equality for comparison

   Replace = with === to compare value and type correctly.

3. Final Answer:

   Should use === instead of = -> Option C

4. Quick Check:

   Use === for comparison, not = [OK]

Hint: Use === for comparison, = is assignment [OK]

Common Mistakes:

• Using = instead of == or ===
• Ignoring variable declaration
• Assuming no error in if condition

5. You want to check if a variable score is between 50 and 100 inclusive. Which expression correctly uses comparison operators to do this?

hard

A. score >= 50 && score <= 100

B. 50 <= score <= 100

C. score > 50 || score < 100

D. score == 50 && score == 100

Solution

1. Step 1: Understand range checking in JavaScript

   JavaScript does not support chained comparisons like 50 <= score <= 100 as in math.

2. Step 2: Use logical AND with two comparisons

   Use score >= 50 && score <= 100 to check both conditions separately.

3. Final Answer:

   score >= 50 && score <= 100 -> Option A

4. Quick Check:

   Use && with two comparisons for range [OK]

Hint: Use && with two comparisons for ranges [OK]

Common Mistakes:

• Using chained comparisons like 50 <= score <= 100
• Using || instead of &&
• Checking equality to both ends simultaneously