Comparison operators in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the == operator do in JavaScript?

The == operator compares two values for equality, allowing type conversion if needed. For example, 5 == '5' is true because the string '5' is converted to number 5 before comparison.

beginner

What is the difference between == and ===?

== checks for equality with type conversion, while === checks for equality without type conversion (strict equality). So 5 == '5' is true, but 5 === '5' is false.

beginner

What does the != operator do?

The != operator checks if two values are not equal, allowing type conversion. For example, 5 != '6' is true because 5 is not equal to 6 after conversion.

beginner

How do the < and > operators work?

The < operator checks if the value on the left is less than the value on the right. The > operator checks if the left value is greater than the right value. Both compare numbers or strings based on Unicode order.

beginner

What is the purpose of <= and >= operators?

The <= operator checks if the left value is less than or equal to the right value. The >= operator checks if the left value is greater than or equal to the right value.

What will 5 == '5' return in JavaScript?

A undefined

B false

C TypeError

D true

== compares values with type conversion, so '5' is converted to number 5, making the comparison true.

Which operator checks equality without type conversion?

A !=

B ===

C ==

D <=

=== checks strict equality, meaning both value and type must be the same.

What does 10 >= 10 evaluate to?

A true

B TypeError

C undefined

D false

>= means greater than or equal, so 10 is equal to 10, making it true.

What is the result of 'apple' < 'banana'?

A false

B TypeError

C true

D undefined

Strings are compared by Unicode order. 'apple' comes before 'banana', so it is true.

Which operator means 'not equal' with type conversion?

A !=

B !==

C ===

D ==

!= checks if values are not equal, allowing type conversion.

Explain the difference between == and === operators in JavaScript.

Think about how JavaScript treats types when comparing.

List and describe the main comparison operators used to compare numbers or strings in JavaScript.

Focus on operators that compare values and their meanings.

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