If you downloaded a version of the full example complete source code, depending on when downloaded, you may have a few lines in the file to delete. Then please follow the step below.
Also, these lines have now been removed from the "complete example source code" in the "full example", so if you have not started coding yet, you could just re-download that source code.
Remove Lines
Search the model.js file for "Tripler". If you find these lines shown (starting about line 81), they can simply be deleted (and then resave the file).
If you do not find any references to Tripler, then you should be all set (nothing to do).
//------------------------//Object Play Script
let n;
n = new Tripler(10);
prn(n.toString());
n.triple();
prn(n.toString());
n.triple();
prn(n.toString());
n.one();
prn(n.toString());