I assume you mean:

  var tester = test();
  tester();

And yeah I agree, straight functions seem way nicer, which is what the coroutine() wrapper in the writeup ends up accomplishing.

Javascript 1.7 copied the generator/coroutine objects straight from Python, and it's a weird fit...

One thing that you can't do with just a function is have the .close() method, which may or may not be a fundamental issue.