If you like JavaScript Koans you might enjoy my newer, more user friendly, project Didacto: JavaScript
JavaScript Koans is an interactive learning environment that uses failing tests to introduce students to aspects of JavaScript in a logical sequence.
The inspiration for this project comes from the Edgecase Ruby Koans and the book 'Javascript: The Good Parts'.
Open the file jskoans.htm in your favourite browser and make the tests pass.
The koans use the Qunit test syntax and test runner.
Get started with Ryan Anklam's Learn JavaScript completely On the Cloud With the JavaScript Koans and Cloud9 IDE