Number API: Number.isNaN()

The function Number.isNaN()

• is a static function on Number

returns false

for any not-Number type

• like null
• like a string
• like an object

different to the global isNaN function (specified in ES1)

• an object gets converted to a Number before the check, and returns true therefore
• a string gets converted to a Number first, and returns true therefore (even though its not NaN)

for real Numbers

• like 0
• or Infinity (+∞)
• or the biggest Number (9007199254740991 (2^53−1))
• or a decimal number

returns true for

• exactly NaN
• the result of zero divided by zero
• something which seems not to be a number

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.