JavaScript powered Light Theremin

I made a light theremin -- basically the same as in the Starter Kit tutorial book, but I've extended it so that it plays discrete tones (a common scale á la C, C#, D, D#, etc.).

Additionally, I wrote a simple HTML page and some JavaScript code, that changes the brightness of the computer's monitor, so that I can play music with the light theremin by "reading the song from the screen".

Check out my blog, that contains a video:

The source code is on GitHub:

Very basic, but hopefully an inspiration for someone else!

I am new in this forum I do not know where i should post this. I am having a problem, i think a very simple one but am not able to solve it. when i write the code and verify, it returns error message in line 2