There's an argument to be made for a tradeoff between legacy device support and cleaning up cruft, but the part that stands out to me is that optional chaining

There's an argument to be made for a tradeoff between legacy device support and cleaning up cruft, but the part that stands out to me is that optional chaining is such a trivial thing to break backwards compatibility over. It's one thing to require async/await: transpiling async->generators->regenerator turns into loads of ugly/inefficient code. But optional chaining saves a couple dozen characters, and if the developer really wanted it they could add a very simple babel transform. Having seen code break over this exact thing before, I'm almost certain that the developer was unaware they were breaking anything for anyone.