Number.isNaN

The Number.isNaN() method determines whether the passed value is NaN. It is a more robust version of the original, global isNaN().

Syntax

Number.isNaN(value)

Parameters

value

The value to be tested for NaN.

Return value

A Boolean indicating whether or not the given value is NaN.

Description

Due to both equality operators, == and ===, evaluating to false when checking if NaN is NaN, the function Number.isNaN() has become necessary. This situation is unlike all other possible value comparisons in JavaScript.

In comparison to the global isNaN() function, Number.isNaN() doesn't suffer the problem of forcefully converting the parameter to a number. This means it is now 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 type number, that are also NaN, return true.

Examples

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

// e.g. these would have been true with global isNaN()
Number.isNaN('NaN');      // false
Number.isNaN(undefined);  // false
Number.isNaN({});         // false
Number.isNaN('blabla');   // false

// These all return false
Number.isNaN(true);
Number.isNaN(null);
Number.isNaN(37);
Number.isNaN('37');
Number.isNaN('37.37');
Number.isNaN('');
Number.isNaN(' ');

Polyfill

Number.isNaN = Number.isNaN || function(value) {
    return typeof value === 'number' && isNaN(value);
}

// Or
Number.isNaN = Number.isNaN || function(value) {     
    return value !== value;
}

Specifications

Specification	Status	Comment
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Number.isnan' in that specification.	Standard	Initial definition.
ECMAScript 2017 Draft (ECMA-262) The definition of 'Number.isnan' in that specification.	Draft

Browser compatibility

See also

• Number
• isNaN()