# Understanding NaN in Typescript

## What is NaN?

NaN stands for “not a number”. It is a value of the number data type in JavaScript, which represents a value that is not a valid number.

NaN is usually returned when a mathematical operation fails to produce a valid number or when a function that expects a number argument is passed a non-numeric value.

## NaN in Typescript

Like in JavaScript, NaN has a special meaning in TypeScript too. It is a value of the number data type that represents a value that is not a valid number.

The following code demonstrates how NaN can be used in TypeScript:

let x: number = 5;

let y: number = NaN;

let z: number = x + y; // z will be NaN

## Checking for NaN

NaN is not equal to any other value, including itself. Therefore, the usual equality operators (== and ===) cannot be used to check if a value is NaN.

The recommended way to check if a value is NaN is to use the built-in isNaN() function, as shown below:

let x: number = NaN;

if (isNaN(x)) {

console.log("x is NaN");

}

## FAQs

### Q: What is the difference between NaN and undefined?

A: NaN is a value of the number data type that represents a value that is not a valid number. Undefined, on the other hand, indicates a variable that has been declared but has not been assigned a value. NaN is a specific value, whereas undefined is a type of variable state.

### Q: What is the difference between NaN and null?

A: NaN is a value of the number data type that represents a value that is not a valid number. Null, on the other hand, is a special keyword in JavaScript that represents a deliberate non-value or absence of any object value. NaN is a specific value, whereas null is a keyword that can represent any data type.

### Q: Is NaN a global variable?

A: No, NaN is not a global variable in JavaScript or TypeScript. It is a value of the number data type that is predefined in both languages.