It’s certainly possible, but I worry that weird things can happen when doing something as “simple” as defining a property if another thread is messing with the prototype chain. Even thread safe property maps can’t entirely save you because operations that need to go up the prototype chain are not and cannot be atomic.
Yes, you did. And it's a good design. You even did the GC question justice.
My concern is more in the spirit of "Your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.". Of course JS being single threaded wasn't a hard constraint. Lift it, and people like you can use the parallelism to do great things.
The problem is that most developers are not you. Shared memory concurrency is foot-artillery (especially if truly parallel). Adding threads to the JS ecosystem is selling W48 nuclear artillery shells at the toy store.
JS's ostensible limitation to a single thread forced users to do what they should have been doing anyway: message-passing, thread-per-core architecture, and actor-ish stuff. People who don't know better reach for shared memory concurrency because it seems like a good way to solve problems, but it's actually a dangerous attractor in idea space. JS engine limitations were accidentally keeping people away from it. Now that they can hear the siren's song of a mutex, they'll run around on the hard problems of parallel programming.
Now, that's not a reason to avoid shipping such a system. It's just not something I would have chosen to implement for the masses.
It's successful because it's been kept away from the kind of programmers who think the time spent to endlessly specify everything four times is nothing compared to the sadness of losing a byte or a cycle. These are the descendants of people who hundreds of years ago would have insisted that real work is in Latin. C++26 is available for them, or Node/React with hundreds of dependencies if they want JavaScript, or they can even compile and run whole operating systems into WASM now, or anything else. Just let JavaScript be the domain of people who do other things for fun.
I think with ES6 and newer things really cleaned up and now we’re left with avoidable ugly parts, of which every language has.
Before when you didn’t even have strict equality checking, for example, you were forced to know about implicit type casting.
Getting on the same page with modules also helped a lot. Typescript directly in Node is great. Look mom, no build system!! I’m just hoping one day browsers will accept TS the same way.
There’s a mode to pretend those features don’t exist and not allow them. Meaning it gets far simpler to just type elide rather than any actual compilation effort. I think this idea is getting more popular and it would be kinda nice if TS committed to not adding any more features like that.