Support es7 exponation operator

[fdecampredon]

https://github.com/rwaldron/exponentiation-operator I don't think it needs proposal.
Few emitting examples :

x**y 
Math.pow(x,y)

x **= y 
x = Math.pow(x, y);

[RyanCavanaugh]

Creating an ES7 label 😄

What happens if Math is shadowed in the current scope? Error?

[fdecampredon]

What happens if Math is shadowed in the current scope? Error?

I guess, a more sophisticated solution could be to capture pow in some way before Math gets shadowed but it's not really necessary in my opinion. Shadowing Math is not so common....

[basarat]

What happens if Math is shadowed in the current scope

error 👍

[DanielRosenwasser]

I'm sure we could just perform some appropriate tests to see if Math.pow is working correctly. (Note: this is a joke)

error 👍

That's a rather untraditional direction to take. We don't currently take that approach with String in certain places where it might be more convenient or efficient to do so. On the other hand, I think the alternative would be __exponentiate, __exp, or __pow.

[fdecampredon]

@DanielRosenwasser you want to check if Math.pow return a fine result if Math has been shadowed ?

[DanielRosenwasser]

Sorry, you'll have to forgive me, that was a joke. I've amended my comment to clarify it.

[fdecampredon]

No that's me sorry, since my english is far from being perfect I often fail to understand what is a joke in some context ^^.

[danquirk]

We obviously want/will support this when the time comes but given how early it is in ES7's development process we'd rather close this and wait on locking down exactly what ES7 is doing. As we've always said, ending up misaligned with a future ES version is our worst case scenario. Although it may be quite likely this ends up in ES7 as currently spec'd the risk of that not being the case isn't enough to add this to TypeScript today given the relatively low value of this operator.

[RyanCavanaugh]

Once ES7 decides the exact syntax here (I could see ^^ or ** happening) and whether or not it's exactly equivalent to Math.pow, we can revisit this to see about downlevel emit.