Added default every/all iterator as _.identity for consistency with any/some

[lennym]

It struck me as odd that _.all needed an iterator to be defined, but _.any defaulted to identity. It seems to me that these methods should be consistent with one another.

[braddunbar]

Hey @lennym, thanks for your pull request! This has actually been discussed before in #218. Since ES5 specifies that the iterator is not optional and Underscore provides a fallback, we should stick to being compatible with the upstream API.

If IsCallable(callbackfn) is false, throw a TypeError exception.

[lennym]

I assume the default iterator in _.any is just for backwards compatibility then, since ES5 some also requires an iterator?

It just seems slightly odd to (as mentioned in #218) break backwards compatibility in favour of upstream compatibility in one instance and not another.

[braddunbar]

Good point, I should've looked closer before dismissing as a duplicate. :)

@jashkenas Any reason not to mirror any/some here?

[jdalton]

Any reason why my comment was deleted?

It was smth like

The whole ES5 thing is beside the point because this is done before the native method call. I think it's odd Underscore will hold up spec on non-consistency issues like this but throw it under the bus for others like sparse array support where there is actually a real consistency issue between native vs. fallback implementations.

To which @braddunbar replied "Good point, I should've looked closer before dismissing as a duplicate. :)".

[jashkenas]

Yep -- having the iterator default to identity is pretty damn useful. Merging.