typeof Infinity and typeof Number.Infinity

[Christoph Bussler]

Hi,

as expected, typeof Infinity is 'number'. However, typeof Number.Infinity is 'undefined'. Why is that?

typeof Number.POSITIVE_INFINITY and typeof Number.NEGATIVE_INFINITY are both 'number', too. So I would expect typeof Number.Infinity to be 'number' also.

Thanks.

[Paul Harris]

I may be wrong, but 'Infinity' is like null and Undefined - a magic reserved word.

It is not a property of the 'Number' object,

So Number.Infinity is Undefined in the same way as Number.whatever

"whatever" is not a property on Number either, so it is also Undefined.

[Rick Waldron]

On Wed, Dec 5, 2012 at 9:36 PM, Paul Harris <harr...@gmail.com> wrote:

I may be wrong, but 'Infinity' is like null and Undefined - a magic reserved word.

It is not a property of the 'Number' object,

Confirmed. There is no such property of the global Number object.

Rick

So Number.Infinity is Undefined in the same way as Number.whatever

"whatever" is not a property on Number either, so it is also Undefined.

On Thursday, December 6, 2012 8:41:57 AM UTC+8, Christoph Bussler wrote:

Hi,

as expected, typeof Infinity is 'number'. However, typeof Number.Infinity is 'undefined'. Why is that?

typeof Number.POSITIVE_INFINITY and typeof Number.NEGATIVE_INFINITY are both 'number', too. So I would expect typeof Number.Infinity to be 'number' also.

Thanks.

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[chbussler]

Thanks for the quick reply. WebStorm suggests in the auto completion that it is. I'll circle back with them on that.

[Yang Guo]

The ECMA-262 5.1 spec expects the Number object to have the properties MAX_VALUE, MIN_VALUE, NAN, POSITIVE_INFINITY and NEGATIVE_INFINITY. Any other property is therefore undefined, so that (Number.Infinity === undefined) evaluates to true.

Yang