Yes, even though the Javascript was written using Doubles and the WASM was written using 64 bit ints. It just means that it's possible to write optimized Javascript (mainly by reducing object allocations, reuse objects instead)
Of course it is always possible to write highly optimised code. But that’s not what people actually do, because of time, skill and maintenance constraints. Here’s a case study: in 2018 Mozilla ported some code from JS to Rust + WASM and got a 6x speed up [1]. An expert in V8 responded to this with highly optimised JavaScript, saying Maybe you don't need Rust and WASM to speed up your JS [2]. Both articles are worth reading! But it is worth remembering that it’s a lot quicker and easier to write the code in #1 than #2 and it is easier to maintain as well.
[1] - https://hacks.mozilla.org/2018/01/oxidizing-source-maps-with...
[2] - https://mrale.ph/blog/2018/02/03/maybe-you-dont-need-rust-to...
Performance sucked when I used native Javacsript BigInts. When I made my own BigInt by using an array of doubles, and pretended that the doubles were 48-bit integers, performance was much better. Using the arrays meant that all allocation of temporary values completely stopped. I had to write my own multiply-and-add function that would do bigint = bigint * 48-bit number + other bigint + other 48-bit number.