The fairly unique thing about the web is that the tech stack is pretty much entirely dependent on what browsers are "winning" at any given time. There are web standards, but Chrome steamrolls them regularly (either by ignoring them or by pressuring the committee to standardize what they want). This is why browser monoculture is bad, and why people recommend Firefox and other non-Chrome (or really, non-WebKit) browsers, as a matter of principle.

So right now, with Chrome's dominance, Mozilla's struggles, and the extremely slow progress of WebAssembly and WASI, it definitely feels like JavaScript will remain dominant for a long while. But since Chrome does support WebAssembly and Google participates in WASI, and since there's no fundamental reason why WASI can't eventually provide everything that JS does today, there's good reason to expect the JS stranglehold not to last forever.

And the great thing about WASM/WASI is that, since it's designed as a compilation target rather than a language, there won't be any remaining reason for a single language (such as Rust) to dominate. Rust got an early lead in WASM because they put the effort into making it a viable target platform for the compiler, and because it's the kind of language that attracts people who dislike JavaScript (such as myself). But there's no reason a different language couldn't rapidly become the most commonly used WASM language if, say, a web framework in a previously-niche language becomes popular. (After all, Rails, a back-end framework, is what popularized Ruby.)

Edit to add: I say "fairly unique", but in fact there's a very analogous situation with C: https://faultlore.com/blah/c-isnt-a-language/