John Resig - Redefining the Introduction to Computer Science
The environment is built around a two-panel view: The left being an Ace editor and the right being a canvas.
All of the user’s code is written using JavaScript and uses Processing.js to generate all the graphics.
All code is executed in real-time. Not only is the code re-run but the code that you change is live dynamically injected into the runtime — this gives you the ability to change variables, colors, or even functions on the fly without the program ever restarting.