Use const/let instead of var

[mjackson]

I've been bitten one too many times by var. Let's use const/let instead.

[oguzbilgic]

This sounds like good first-timer. I can give this a try if no one else is working on it.

[knowbody]

that's great @oguzbilgic, thanks!

[mjackson]

Ooops, sorry @oguzbilgic! I didn't see your comment until after I had already done the work. :(

Let's make a first-timer label so it'll be easy for people to find them in the future.