Comparison operators in Javascript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of chained comparison with mixed types

What is the output of this JavaScript code?

console.log(3 < 4 < 5);

Javascript

console.log(3 < 4 < 5);

A TypeError

B undefined

C false

D true

💡 Hint

Remember that JavaScript evaluates comparisons from left to right and converts booleans to numbers in some cases.

The expression 3 < 4 is true, which converts to 1 when compared to 5. Then 1 < 5 is true, so the final output is true. But the code is console.log(3 < 4 < 5), which evaluates as (3 < 4) < 5 → true < 5 → 1 < 5 → true. So the output is true, but the question asks for the output of the code exactly. The code outputs true, so option D is correct.

❓ Predict Output

intermediate

Output of strict equality with different types

What is the output of this JavaScript code?

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

Javascript

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

A true

B false

C TypeError

D undefined

💡 Hint

Strict equality checks both value and type.

The string '5' and the number 5 have different types, so strict equality === returns false.

❓ Predict Output

advanced

Output of comparing objects with == and ===

What is the output of this JavaScript code?

const a = {};
const b = {};
console.log(a == b);
console.log(a === b);

Javascript

const a = {};
const b = {};
console.log(a == b);
console.log(a === b);

A false\ntrue

B true\ntrue

C false\nfalse

D true\nfalse

💡 Hint

Objects are compared by reference, not by content.

Both == and === compare object references. Since a and b are different objects, both comparisons return false.

❓ Predict Output

advanced

Output of comparing null and undefined with == and ===

What is the output of this JavaScript code?

console.log(null == undefined);
console.log(null === undefined);

Javascript

console.log(null == undefined);
console.log(null === undefined);

A true\nfalse

B false\nfalse

C true\ntrue

D false\ntrue

💡 Hint

== allows type coercion, === does not.

null == undefined is true because == treats them as equal. null === undefined is false because they have different types.

❓ Predict Output

expert

Output of comparing NaN with itself

What is the output of this JavaScript code?

console.log(NaN == NaN);
console.log(NaN === NaN);
console.log(Object.is(NaN, NaN));

Javascript

console.log(NaN == NaN);
console.log(NaN === NaN);
console.log(Object.is(NaN, NaN));

A false\nfalse\ntrue

B true\ntrue\ntrue

C true\nfalse\nfalse

D false\ntrue\nfalse

💡 Hint

NaN is not equal to anything, even itself, except with Object.is.

NaN == NaN and NaN === NaN both return false. Object.is(NaN, NaN) returns true.

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