JavaScript in an Introduction to Programming course

I'm curious... Why don't more people use JavaScript as an introductory language to new programmers? All the student needs is a web-browser (with JS enabled) and a text editor to get started. With JS, you can practice basic control structures (iterative and conditional), polymorphism, prototyping, inheritance, everything that you would need to go over in a Programming 101 course.

It's common for many educators to teach an introductory course with popular high-level languages such as Ruby and Python. I would love to do the same but throughout the student's education, he/she will most likely be jumping into Java or a C-based language in their next successive course. If thats the case, then why learn Ruby/Python for the time frame of a couple of months? Why go through the bother of installing all of it? I love Python myself as a "new programmer" I would be confused jumping from Python to C or Java.

Choosing JavaScript as an introductory language could do a few things to help out a new student:
- it's already "there" on most computer
- there's no real need to install an IDE
- no need to compile
- the student should have no problem moving into java or c next

Hmm what are the cons?