You have web workers, and for shared memory and synchronisation respectively SharedArrayBuffer and the Atomics namespace.
The only thing you can't do with JS today is share a heap across threads. You have SharedArrayBuffer. You have atomics. You don't need a shared address space.
There's a high performance database called "PostgreSQL" you may have heard about. It doesn't use threads. It uses separate processes and shared memory: just like standard JavaScript, with its service workers and SharedArrayBuffer.
If not sharing an address space is good enough for PostgreSQL, it's good enough for your TypeScript database.
The problem with shared-everything, unmarked, preemptive-parallel concurrency is that 90% of the time it gets used by people who don't know they shouldn't.
Yeah, that sucks, but at least it's just an implementation problem. Java's analogous ByteBuffer methods have been fast compiler intrinsics for a long time, so there's an existence proof of this stuff done right.