Replace Object.prototype.toString.call with Array.isArray about classnames

[dcousens]

@klimashkin you could also just do

object != null && object.constructor === Array

Which is 400% faster again. See https://jsperf.com/array-isarray-vs-instanceof-array/12

[klimashkin]

Yep, but it have a point if you check array.
If it is not array (and commonly we have no array as argument, more common are objects and booleans) faster to use Array.isArray
Because false.constructor === Array is actually means Object(false).constructor === Array

[dcousens]

You're right, however if we just moved the else if (check if Array branch to be last, then it would be taking advantage of the fact that all other options failed, so the assumption that is an Array is therefore more likely.

[klimashkin]

But if we'll make array check the last, we should move check for object above, ie replace 'object' === typeof arg with Object.prototype.toString.call(arg) === '[object Object]' which is slower

[dcousens]

I'll look into it. Haven't had time to check over it thoroughly yet.

[stuartsan]

Mentioned in #24 but also relevant here:

The issue with using instanceof Arrray or thing.constructor === Array is that it may fail when multiple frames are in use, because different frames' constructors have different identities, so frame 1's Array !== frame 2's Array.

[dcousens]

Merged in #24