[lifthrasiir]

> Well, according to the manual, you can by appending '+0.0' (or '.0'?) to numbers, converting it to float.

In addition to making extensive changes to the code, this is not complete because there are plenty of functions that would return integer instead of numbers (e.g. tonumber).

> Perhaps they could have gone for a more separate integer type?

I too think JS did the right thing: it introduced a new type for integers, and took it as a chance to make it arbitrary precision.