Using Tailspin, a flexible and reversible Javascript interpreter, for algorithm visualisation merely scratches the surface of what it can do.

One of the more interesting opportunities is interactive learning environments. There are many online interactive Javascript websites, but all use the browser’s interpreter or server-side execution of code. Websites like Code Academy and Khan Academy do a pretty good job, but they are limited by the black-box execution of code in the browser.

By using Tailspin which provides access to the inner workings of the interpreter it is possible to expand what can be done in these online interactive coding websites.


Modelled on the pointer programming puzzles of Jhavé, I have used Tailspin to create a small website for interactive Javascript programming problems. Access to Tailspin’s workings during execution allows the visualise of any user supplied program as it runs, and enables them to see how their solution succeeds or fails.

Among other things it provides:

  • Live code errors and warnings
  • A range of programming puzzles
  • Automatic saving of your progress
  • Scrubbable execution of your Javascript program
  • A visualisation of your program running that shows the values and lists in your program
  • A visualisation that animates as you scrub through the program execution

Check it out here: JS problems — How will you fare?