The biggest factor here is that CLJS is interpreted, GC-ed with immutable data structures while Rust is lower level with highly optimized WASM bytecode, that's optimized by Rust/LLVM compiler ahead of time.
So, when there's a lot of terminal activity (high speed colorful animation), the terminal emulator in CLJS implementation allocates and GCs millions of data structures every second. In Rust implementation there's very little allocation because most code operates on already pre-allocated buffers, and just mutates then. Both approaches are standard to their language. I could have tried all sorts of tricks (in fact I tried some) in CLJS to make this implementation faster but it would very quickly make the code non-idiomatic, and not fun to work with. But let's say I could make the CLJS impl be on par with a theoretical plain JS impl - this would likely still be many times slower than a basic Rust impl. Modern JS engines are amazing but they just can't beat WASM. Maybe some day :)
And yet it is.
The biggest factor here is that CLJS is interpreted, GC-ed with immutable data structures while Rust is lower level with highly optimized WASM bytecode, that's optimized by Rust/LLVM compiler ahead of time.
So, when there's a lot of terminal activity (high speed colorful animation), the terminal emulator in CLJS implementation allocates and GCs millions of data structures every second. In Rust implementation there's very little allocation because most code operates on already pre-allocated buffers, and just mutates then. Both approaches are standard to their language. I could have tried all sorts of tricks (in fact I tried some) in CLJS to make this implementation faster but it would very quickly make the code non-idiomatic, and not fun to work with. But let's say I could make the CLJS impl be on par with a theoretical plain JS impl - this would likely still be many times slower than a basic Rust impl. Modern JS engines are amazing but they just can't beat WASM. Maybe some day :)