A plain number is a double, and then the compiler can prove it can be a 64-bit integer if the size is appropriate. The goal is to keep behavior parity with Node here. Loop counters etc stay double. But we also support custom types we introduced such as i32, which is crucial for embedded performance. And then of course we have proper typed arrays.

Regular arrays are dense, but we keep a presence bit for every element so we can identify sparse arrays and differentiate holes from undefined's. And finally, there's no Error.stack support right now.