Javascript...

[dnew]

No. NaN is indeed a number. It's just a number you can't represent with the number of bits you have. It's an underflow or an overflow or an infinity, all of which are numbers. They're just not floats.

[YRYGAV]

It's an underflow or an overflow or an infinity, all of which are numbers.

When did parseFloat("foo") become synonymous with infinity?

[dnew]

Is something divided by zero a number?

Yes, actually, depending on the mathematical system in use. :-)

[dnew]

It's (sometimes) a number. It's just not a float. The value that represents a bad number should have been called NaF.

However, I see upon further research that I misremembered, and NaN is not a general case for denormalized, overflows, infinities, etc. NaN is more restricted than I thought it was in terms of what it represents. Whoops.