What Is NaN Property in JavaScript #6

Hello readers, We have covered five questions from my front-end interview questions series until now, and today we are going to discuss the 6th question of the series.

What is NaN

NaN stands for Not-a-Number, In JavaScript it represents a value that is not valid number. It is a global value meaning it is accessible from anywhere in our code.

How NaN is created?

Let’s see some examples that returns NaN.

Dividing zero by zero

console.log(0 / 0);

Taking the square root of a negative number

console.log(Math.sqrt(-2)); // NaN

Trying to convert non-numeric values to numbers (e.g., “hello” to a number)

console.log(parseInt("hello")); // NaN

Performing arithmetic operations with infinity

console.log(0 * Infinity); // NaN
console.log(1 ** Infinity); // NaN
console.log(Infinity / Infinity); // NaN
console.log(Infinity - Infinity); // NaN

Other arithmetic operations

console.log("hello" - 2); // NaN
console.log("hello" * 2); // NaN
console.log("hello" / 2); // NaN

Characteristics of NaN

When we compare NaN to NaN it returns false 😅

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

console.log(NaN !== NaN); // true
console.log(NaN != NaN); // true

Checking for NaN

We use isNaN function to check if the provided value is non-numeric

console.log(isNaN("Hello")); // true
console.log(isNaN(NaN)); // true
console.log(isNaN(12)); // false
console.log(isNaN("12")); // false

For more precise checks, we use Number.isNaN(). It was introduced in ES6.

console.log(Number.isNaN(NaN)); // true
console.log(Number.isNaN(12)); // false
console.log(Number.isNaN("12")); // false

Number.isNaN() returs false for all values except NaN.

isNaN() convert the provided value to number before checking if it is NaN, on the other hand Number.isNaN() does not perform any type conversion. It strictly checks if the provided value is NaN without trying to convert it.

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Happy Coding 🙌 !