Javascript doesn't change at anything like the pace that TypeScript does, so it hasn't been much of a hassle.
But even so we (like many teams with large codebases, I suspect) have callbacks, promises, and async/await all mixed together, depending on when the code was (re)written. It's on our list.
Javascript formally releases once a year, but individual feature adoption in browsers is totally separate from that, and happens.... whenever they feel like it. v8 (chrome's js engine) doesn't have a set release schedule, but has already had 6 formal minor releases this year, each partially adopting some new JS runtime features, all of which have already shipped to chrome.
At our current pace, we formally release 4 times a year, for reference, which is actually a far cry from the more continuous deployment browser vendors currently have setup.
The main difference is that most people kinda ignore new JavaScript stuff for awhile until it trends or gains sufficient rollout. It's an interesting world - I can't really say that people are actually JavaScript version aware, beyond, maybe, what compatibility presets @babel/preset-env gives them.
But even so we (like many teams with large codebases, I suspect) have callbacks, promises, and async/await all mixed together, depending on when the code was (re)written. It's on our list.