If you're using ES6 you may as well use spread and defaults to make it more useful:

const $ = (selector, context=document) => [...context.querySelectorAll(selector)]

Or just polyfill it with NodeList.prototype.forEach = Array.prototype.forEach and get nice readable code.

Point is: we shouldn't have to.

Vanilla JS also allowed you to look inside HTML5 FormData a few months earlier. And no, it isn't FormData.toString().