In this article, we will learn what does NaN mean in JavaScript programming with code example.

In JavaScript, NaN stands for “Not a Number.” It’s a special value that represents the result of an undefined or unrepresentable mathematical operation, such as the square root of a negative number, or the result of trying to parse an invalid number from a string.

For example, the following code will return NaN:

parseFloat("not a number"); // NaN

Math.sqrt(-1); // NaN

It’s important to note that NaN is a unique value in JavaScript, meaning that NaN is not equal to any other value, including itself. So the following comparison is not working as it should

if (value === NaN) {
  // This block will not execute if value is NaN
}

To check if a value is NaN you can use the function isNaN(value)

if (isNaN(value)) {
  // this block will execute if value is NaN
}

Another way to check NaN values is the Number.isNaN(value) it introduced in ES6 that is more accurate than the global isNaN()

if (Number.isNaN(value)) {
  // this block will execute if value is NaN
}

It’s important to note that in Javascript NaN is of type number, it’s a number but a special one, that you should take care when working with it.

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