Question

I found a difference in the handling of

[1,2,3].slice(1, undefined)

between chrome (that returns [2,3]) and firefox (that returns []).

Both of course instead agree on [2, 3] as the value of

[1,2,3].slice(1)

and they also both agree on [] as the value of

[1,2,3].slice(1, null)

Which of the two is correct? Or may be this not clearly specified in the standard?

Answer 1

The specification says:

7. If end is undefined, let relativeEnd be len; else let relativeEnd be ToInteger(end).

Which Firefox version are you using? Firefox 5 gives me correctly [2, 3]. Update: Firefox 3.6 returns indeed an empty array.

I don’t know what is wrong here, because if you call slice() without a second parameter, end will be undefined too.

Update:

After playing around a bit, it seems that an empty array is returned if the second parameter passed to .slice() is NaN. Example (+undefined returns NaN):

> [1,2,3].slice(1, +undefined)
> []

This is the same in Firefox and in Chrome.

Unfortunately, this is also not conform to the specification, as ToInteger(NaN) ^[spec] should return 0, so the the array should actually be sliced to the end.

I don’t claim that this is the reason why it does not work properly in some Firefox versions, I don’t know the implementation.

Incident of minor disorientation… never mind.