Adding a static type system to JavaScript would have, IMO, been a losing effort. You can take a look at ActionScript 3 for an example of the challenges that come up.
Once you've got a static type system, you need a GOOD static type system, and imposing one of those on JS without breaking backwards compatibility would have been an ordeal and complicated code tremendously.
Once you've got a static type system, you need a GOOD static type system, and imposing one of those on JS without breaking backwards compatibility would have been an ordeal and complicated code tremendously.