For Testing your Javascripts, try Testem - a new tool for Javascript Test-Driven-Development (TDD) and Continous Integration (CI).
To get started, you first need to create a room and connect your browser to it. Once a room is created you can connect other browsers to it as well.
Then, to go further, follow the instructions for using the driver.
When you enter a Javascript command, it is immediately sent to each browser that's connected to the room. Each browser then eval()
the Javascript within an iframe sandbox and then send the result back to be displayed.
Communication happens in real-time thanks to the brilliant Socket.IO which puts a nice abstraction around WebSocket and Comet techniques.
Ping me on twitter @airportyh or submit an issue on GitHub.