The global NaN
property is a value representing Not-A-Number.
Property attributes of NaN |
|
---|---|
Writable | no |
Enumerable | no |
Configurable | no |
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Description
NaN
is a property of the global object. In other words, it is a variable in global scope.
The initial value of NaN
is Not-A-Number — the same as the value of Number.NaN
. In modern browsers, NaN
is a non-configurable, non-writable property. Even when this is not the case, avoid overriding it. It is rather rare to use NaN
in a program.
There are five different types of operations that return NaN
:
- Number cannot be parsed (e.g.
parseInt("blabla")
orNumber(undefined)
) - Math operation where the result is not a real number (e.g.
Math.sqrt(-1)
) - Operand of an argument is NaN (e.g.
7 ** NaN
) - Indeterminate form (e.g. 0 *
Infinity
) - Any operation that involves a string and is not an addition operation (e.g. "foo"/3)
Examples
Testing against NaN
NaN
compares unequal (via ==
, !=
, ===
, and !==
) to any other value -- including to another NaN value. Use Number.isNaN()
or isNaN()
to most clearly determine whether a value is NaN. Or perform a self-comparison: NaN, and only NaN, will compare unequal to itself.
NaN === NaN; // false Number.NaN === NaN; // false isNaN(NaN); // true isNaN(Number.NaN); // true Number.isNaN(NaN); // true function valueIsNaN(v) { return v !== v; } valueIsNaN(1); // false valueIsNaN(NaN); // true valueIsNaN(Number.NaN); // true
However, do note the difference between isNaN()
and Number.isNaN():
the former will return true
if the value is currently NaN
, or if it is going to be NaN
after it is coerced to a number, while the latter will return true
only if the value is currently NaN:
isNaN('hello world'); // true Number.isNaN('hello world'); // false
Additionally, some array methods cannot find NaN, while others can.
let arr = [2, 4, NaN, 12]; arr.indexOf(NaN); // -1 (false) arr.includes(NaN); // true arr.findIndex(n => Number.isNaN(n)); // 2
Specifications
Specification |
---|
ECMAScript (ECMA-262) The definition of 'NaN' in that specification. |
Browser compatibility
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
NaN | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 4 | Opera Full support 4 | Safari Full support 1 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 10.1 | Safari iOS Full support 1 | Samsung Internet Android Full support 1.0 | nodejs Full support 0.1.100 |
Legend
- Full support
- Full support