More critiques

[domenic]

In addition to #3:

• More const, less let, and never use var in ES6.
• No need for parens for single-argument arrow functions.
• Put 'use strict' at the top (although this will be unnecessary once you move to modules).
• Use .js instead of .es6.

In addition I just want to strongly second the use of shorthand object literals recommended in #3. After the var/let usage, that was the biggest thing that stood out to me.

[addyosmani]

Thanks @domenic! We really appreciate the feedback and suggestions. We can definitely move to shorthand object literals.

[domenic]

I think this is mostly done, I'll (re)open any specific critiques.