1) Wow, I didn't know that existed.

2) Wow, those downsides are insane. It's not constant time, thus can't be used in cryptography...? Has huge performance impacts and can't be casted to a "number"- how is this implemented? it can't be native INTs on the CPU?

Any cryptography is surely using Uint8Array.

>Any cryptography is surely using Uint8Array.

Is this to optimise memory operations over a large plaintext/cipher text or is there some other advantage to it that is less obvious (e.g. more resistant to timing attacks?)

No, it’s because Number is internally floating point and cannot represent all integers.