JavaScript 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.
NaN is a Number
The type of NaN is number.
This may look strange, but NaN belongs to the JavaScript number type.
Numeric Strings
JavaScript tries to convert numeric strings to numbers in arithmetic operations.
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.
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);
Try it Yourself »
NaN is Not Equal to Itself
NaN is the only JavaScript value that is not equal to itself.
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;
Try it Yourself »
Note
NaN means Not a Number.
But the type of NaN is number.
Use isNaN() to check if a value is NaN.
