On Fri, Jul 12, 2013 at 10:48 AM, Allen Wirfs-Brock
<allen at wirfs-brock.com> wrote:
> On Jul 12, 2013, at 10:27 AM, Tab Atkins Jr. wrote:
>> On Fri, Jul 12, 2013 at 10:19 AM, Mark S. Miller <erights at google.com> wrote:
>>> No. Even if toInteger meant "no fractional component", I would still expect
>>> it only to return true if there is some specific mathematical integer that
>>> the JS number can be said to exactly represent. For the same reason, I think
>>> isInteger(-0) should be true and isInteger(NaN) should be false.
>>
>> Agreed.  isInteger() has one job, and it's kinda worthless if it can't
>> even do that.  How it should be:
>>
>> Number.isInteger(-0) == true
>> Number.isInteger(NaN) == false
>> Number.isInteger(Infinity) == false
>>
>> And, because of what we discussed in the recent thread...
>>
>> Number.isInteger(Math.pow(2,53)-1) == true
>> Number.isInteger(Math.pow(2,53)) == false
>
> In other words you want to define Number.isInteger to return true only if it's argument is an integer number in the range -(2^53-1)..2^53-1
>
> That's a useful test and a plausible definition of Number.isInteger but it will also probably be surprising to programmers who are familiar with the esoterics of IEEE floats.

On the other hand, people (like me) who just want to be able to tell
when something is a freaking integer will be better served by these
semantics.  ^_^

> If we went that direction what should Number.toInteger do for values outside that range?

The internal operation just returns 0 for things that aren't integers.
 I'd be okay with that, I suppose.  (I use a similar function in some
of my own code, and return false from the operation when the number
cant' be converted, but that's because I use it as a combination
tester and converter.  We have an explicit tester, so I'm fine with
the converter hiding details of its conversion.)

~TJ

On Fri, Jul 12, 2013 at 10:48 AM, Allen Wirfs-Brock <allen at wirfs-brock.com> wrote:

> In other words you want to define `Number.isInteger` to return `true` only if it's argument is an integer number in the range -(2^53-1)..2^53-1
>
> That's a useful test and a plausible definition of `Number.isInteger` but it will also probably be surprising to programmers who are familiar with the esoterics of IEEE floats.

On the other hand, people (like me) who just want to be able to tell
when something is a freaking integer will be better served by these
semantics.  ^_^

> If we went that direction what should `Number.toInteger` do for values outside that range?

The internal operation just returns `0` for things that aren't integers.
 I'd be okay with that, I suppose.  (I use a similar function in some
of my own code, and return `false` from the operation when the number
cant' be converted, but that's because I use it as a combination
tester and converter.  We have an explicit tester, so I'm fine with
the converter hiding details of its conversion.)