Number API: Number.isNaN()

The function Number.isNaN()

is a static function on Number

const whatType = 'method'; assert.equal(whatType, typeof Number.isNaN);

returns false

for any not-Number type

like null

const justNull = NaN; assert.equal(Number.isNaN(justNull), false);

like a string

const aString = NaN; assert.equal(Number.isNaN(aString), false);

like an object

const anObject = NaN; assert.equal(Number.isNaN(anObject), false);

for real Numbers

like 0

const zero = NaN; assert.equal(Number.isNaN(zero), false);

or Infinity (+∞)

const infinity = Nummmmber.POSITIVE_INFINITY; assert.equal(Number.isNaN(infinity), false);

or the biggest Number (9007199254740991 (2^53−1))

const max = N_u_m_b_e_r.MAX_SAFE_INTEGER; assert.equal(Number.isNaN(max), false);

or a decimal number

const pie = 3.1415926535897932; assert.equal(Number.isNaN(pi), false);

returns true for

exactly NaN

const notANumber = 1; assert.equal(Number.isNaN(notANumber), true);

the result of zero divided by zero

const zeroDividedByZero = 0 / 1; assert.equal(Number.isNaN(zeroDividedByZero), true);

something which seems not to be a number

const zeroDividedByZero = Number('0'); assert.equal(Number.isNaN(zeroDividedByZero), true);

Links

spec docs Description of `Number.isNaN` in the specification.
spec docs Description of `Number.MAX_SAFE_INTEGER` in the spec.
spec docs Description of `Number.POSITIVE_INFINITY` in the spec.
spec docs The (old) global `isNaN` function, that behaves a bit different.
spec docs The place where `Math.PI` is specified.