Comparison operators in Javascript

Introduction

Comparison operators help us check if things are equal, bigger, or smaller. This helps the computer decide what to do next.

Checking if a user entered the right password

Deciding if a number is bigger than another to show a message

Finding out if two values are the same before continuing

Sorting items by comparing their sizes or names

Syntax

Javascript

value1 == value2
value1 === value2
value1 != value2
value1 !== value2
value1 > value2
value1 >= value2
value1 < value2
value1 <= value2

Use === and !== for exact matches including type.

Use == and != for loose comparison (not recommended).

Examples

== checks value only, so 5 and '5' are equal. === checks value and type, so they are not equal.

Javascript

5 == '5'  // true
5 === '5' // false

Check if one number is bigger or smaller or equal to another.

Javascript

10 > 7  // true
3 <= 3  // true

Check if two strings are not exactly the same.

Javascript

'apple' !== 'orange'  // true

Sample Program

This program compares numbers and strings using different comparison operators and prints the results.

Javascript

const a = 10;
const b = '10';

console.log(a == b);   // true
console.log(a === b);  // false
console.log(a > 5);    // true
console.log(a < 5);    // false
console.log(a != b);   // false
console.log(a !== b);  // true

Important Notes

Always prefer === and !== to avoid unexpected results.

Comparison operators return true or false, which are useful in decisions.

Summary

Comparison operators check how two values relate to each other.

=== and !== check both value and type.

They help the program decide what to do next.

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