The always entertaining and informative Magnar Sveen has a new episode of Emacs Rocks! up. In Episode 11 he demonstrates swank.js a package that brings the JavaScript REPL to Emacs in much the same way that swank brings us the Common Lisp REPL.
If you are a JavaScript programmer and aren’t already using swank-js you should view Sveen’s video without delay. He shows a simple animation of a bouncing ball and then makes changes to the code that are immediately reflected in the animation. This is good stuff.