Number.isNaN()

{{JSRef}}

The Number.isNaN() static method determines whether the passed value is the number value {{jsxref("NaN")}} , and returns false if the input is not of the Number type. It is a more robust version of the original, global {{jsxref("isNaN()")}} function.

{{InteractiveExample("JavaScript Demo: Number.isNaN()", "taller")}}

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 {{jsxref("NaN")}} .

Return value

The boolean value true if the given value is a number with value {{jsxref("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 {{jsxref("NaN")}} , even if the other operand is also {{jsxref("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 {{jsxref("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 {{jsxref("NaN")}} but aren’t actually the same value as {{jsxref("NaN")}} . This also means that only values of the Number type that are also {{jsxref("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 {{jsxref("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

{{Specifications}}

Browser compatibility

{{Compat}}

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