My first useful JavaScript program

I was recently going through my son's workbook and it had an interest way of teaching addition - probably the Montessori method. The idea was to create a table of sum's of a few numbers and color numbers to see a pattern. I was quite amused and decided to see if I could write the code in JavaScript, a language I am trying to learn, I am going to do some additional work like graphical Towers of Hanoi with it as well, but for now I wanted to start simple

Guess what - I succeeded in writing what I consider as a useful program (although I wrote it quite badly)

Here is the code
Here is the Javascript Here is the output