Hmm, pretty heavy use of ES6, too (async/await, decorators etc.). Is there any "modern" library left that lets you use the browser's JavaScript engine directly, without transpiling?
Neither async/await nor decorators are part of ES6 (which is more properly called ES2015). Almost all major browsers support ES2015. A few recent versions support async/await, now that it's expected for that syntax to be a part of ES2017. None support decorators (in fact, I'd be surprised if decorators ever make it into the formal ES spec).
It's still going to be worth a look, as I don't mind opinionated stuff for some mid-sized SPAs and tools, I'm just missing a tool for the lower end in my belt these days.