_.isNumber(NaN) === true

[limonte]

Feature or bug?

[megawac]

Duplicate of a bunch of issues: https://github.com/jashkenas/underscore/issues?utf8=%E2%9C%93&q=is%3Aissue+is%3Aclosed+nan+isnumber

See jashkenas/underscore#406

[jdalton]

NaN is of the internal tag Number so _.isNumber returns true.
Just as an invalid date object will still return true for _.isDate.

These methods don't validate the input they just determine if the value is of a specific tag.
You may be looking for _.isFinite.

[limonte]

@megawac @jdalton thanks for explanation! Sorry for not-searching before creating the issue :)

[msgoloborodov]

But it is very unexpectedly. NaN is abbreviation of Not a Number. So isNumber(NotANumber) === true seems crazy.

[ephetic]

> typeof NaN
"number"

NaN, Infinity, and 0.22 are all members of the type Number. This isn't even unique to JavaScript. _.isFinite gives you the behavior you want (a Number but not one of those things).

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.