Number.isNaN()

Try it

function typeOfNaN(x) {
  if (Number.isNaN(x)) {
    return "Number NaN";
  }
  if (isNaN(x)) {
    return "NaN";
  }
}

console.log(typeOfNaN("100F"));
// Expected output: "NaN"

console.log(typeOfNaN(NaN));
// Expected output: "Number NaN"

Syntax

Number.isNaN(value)

Parameters

value

The value to be tested for NaN.

Return value

The boolean value true if the given value is a number with value NaN. Otherwise, false.

Description

The function Number.isNaN() provides a convenient way to check for equality with NaN. Note that you cannot test for equality with NaN using either the == or === operators, because unlike all other value comparisons in JavaScript, these evaluate to false whenever one operand is NaN, even if the other operand is also NaN.

Since x !== x is only true for NaN among all possible JavaScript values, Number.isNaN(x) can also be replaced with a test for x !== x, despite the latter being less readable.

As opposed to the global isNaN() function, the Number.isNaN() method doesn't force-convert the parameter to a number. This makes it safe to pass values that would normally convert to NaN but aren't actually the same value as NaN. This also means that only values of the Number type that are also NaN return true.

Examples

Using isNaN()

Number.isNaN(NaN); // true
Number.isNaN(Number.NaN); // true
Number.isNaN(0 / 0); // true
Number.isNaN(37); // false

Difference between Number.isNaN() and global isNaN()

Number.isNaN() doesn't attempt to convert the parameter to a number, so non-numbers always return false. The following are all false:

Number.isNaN("NaN");
Number.isNaN(undefined);
Number.isNaN({});
Number.isNaN("blabla");
Number.isNaN(true);
Number.isNaN(null);
Number.isNaN("37");
Number.isNaN("37.37");
Number.isNaN("");
Number.isNaN(" ");

The global isNaN() coerces its parameter to a number:

isNaN("NaN"); // true
isNaN(undefined); // true
isNaN({}); // true
isNaN("blabla"); // true
isNaN(true); // false, this is coerced to 1
isNaN(null); // false, this is coerced to 0
isNaN("37"); // false, this is coerced to 37
isNaN("37.37"); // false, this is coerced to 37.37
isNaN(""); // false, this is coerced to 0
isNaN(" "); // false, this is coerced to 0

Specifications

Browser compatibility

See also

• Polyfill of Number.isNaN in core-js
• es-shims polyfill of Number.isNaN
• Number
• isNaN()