That's not native 64-bit integers. That's BigInt, and it's already out everywhere, and unless the situation has changed, it's significantly slower than just 64-bit integers would be.
I'm not actually attacking JavaScript for this, note. I don't think it's really all that much of a problem given the purposes of JavaScript, and I think it could really be better fixed by doing something similar to what Lua did, and have all numbers transparently either a 64-bit floating point number or a 64-bit signed integer. If you are using JavaScript and something like specifically needing 64-bit integers is an issue for you, there's a good chance you should just be using WebAssembly.
