This...is incredibly typical of JavaScript's design.

True. I'd argue that it's the best of both worlds: Unlike Java, you have access to a bunch of helpful functions on every primitive, and you can add more by modifying prototypes; and unlike Ruby, primitives are immutable, which puts a cap on the level of complexity (you could write a whole book on Ruby's string objects).

You could do something similar by having each primitive type share a global prototype á la Lua's "string" metatable. Most operations are implemented as primitives in the VM, but any non-primitive operations on primitive types go to the type's metatable.

Well, at least it does the coercion for you (unlike Java).

Good point. I remember trying to work an example in a Java textbook that involved building and printing out a times table. There were so many type coercion errors, I eventually just gave up.