JS could have had support for SIMD and 64 bit it's by now, and progress was actually being made (mostly just through the asm.js experiments), but it was deprioritized specifically to work on WASM.

WASM can even do 32-bit integers, which JavaScript can't, so uses floats instead.

JS has had byte arrays like Int32Array for a while. The JS engines will try to optimize math done into them/with them as integer math rather than float math, but yeah you still can't use an integer directly outside of array math.