js-comint.el: "js-comint.el is a comint mode for emacs which allows you to run a compatible javascript repl such as Spidermonkey or Rhino inside of emacs. At first blush this may seem a little useless, but when paired with Steve Yegge's js2-mode it becomes a useful way of testing non-html-centric javascript code while editing it."
'via Blog this'
