Number.isNaN() vs isNaN() in JavaScript : Explained⚡

This content originally appeared on DEV Community and was authored by Yogesh Bamanier

Learn the difference between Number.isNaN() and isNaN() in JavaScript. This guide explains how each works, why they behave differently, and best practices for checking NaN values.

1⃣ What is NaN?

NaN stands for Not a Number. It represents a value that is mathematically invalid or unrepresentable.

Example:

let result = 0 / 0; // NaN
console.log(result); // NaN

2⃣ isNaN() – The Classic Checker

isNaN() is a global JavaScript function that checks if a value cannot be converted into a number.

console.log(isNaN(NaN)); // true
console.log(isNaN('hello')); // true (string cannot convert to number)
console.log(isNaN(123)); // false

Key Point: isNaN() performs type coercion before checking, which can sometimes give unexpected results.

3⃣ Number.isNaN() – The Modern Approach

Number.isNaN() is more precise. It only returns true if the value is exactly the special NaN value.

console.log(Number.isNaN(NaN)); // true
console.log(Number.isNaN('hello')); // false
console.log(Number.isNaN(123)); // false

Key Point: No type coercion occurs, making it safer for numeric checks.

4⃣ How They Differ

Example Difference:

console.log(isNaN('abc')); // true (string cannot convert to number)
console.log(Number.isNaN('abc')); // false (not the exact NaN)

5⃣ Best Practices for Developers

1. Prefer Number.isNaN() for accurate NaN detection.
2. Use isNaN() when you want to check if a value cannot be interpreted as a number.
3. Remember: NaN is the only value in JavaScript that is not equal to itself.

console.log(NaN === NaN); // false

Conclusion

Understanding the difference between Number.isNaN() and isNaN() helps avoid bugs in numeric validations and ensures your JavaScript code behaves predictably.

Written by Yogesh Bamanier

This content originally appeared on DEV Community and was authored by Yogesh Bamanier