JS NaN

In JavaScript, NaN is short for Not a Number.

NaN is a JavaScript number that is not a legal number.

Invalid Number Operations

You get NaN when JavaScript cannot calculate a number.

Example

let x = 100 / "Apple";

document.getElementById("demo").innerHTML = x;

NaN is a Number

The type of NaN is number.

This may look strange, but NaN belongs to the JavaScript number type.

Example

let x = NaN;

document.getElementById("demo").innerHTML = typeof x;

Numeric Strings

JavaScript tries to convert numeric strings to numbers in arithmetic operations.

Example

let x = 100 / "10";

document.getElementById("demo").innerHTML = x;

Note: The result is 10, because "10" is converted to the number 10.

Non-Numeric Strings

A non-numeric string cannot be converted to a number.

Example

let x = 100 / "Apple";

document.getElementById("demo").innerHTML = x;

Note: The result is NaN, because "Apple" cannot be converted to a number.

Using isNaN()

You can use the JavaScript function isNaN() to find out if a value is not a number.

Example

let x = 100 / "Apple";

document.getElementById("demo").innerHTML = isNaN(x);

NaN is Not Equal to Itself

NaN is the only JavaScript value that is not equal to itself.

Example

let x = NaN;

document.getElementById("demo").innerHTML = x == x;

To test for NaN, use isNaN().

NaN in Math

If you use NaN in a mathematical operation, the result will also be NaN.

Example

let x = NaN;

let y = 5;

document.getElementById("demo").innerHTML = x + y;

Note: NaN means Not a Number. But the type of NaN is number. Use isNaN() to check if a value is NaN.