如何使用onclick来增加JavaScript变量?如何封装JS数组?

I am trying to write a webpage that takes input with an HTML form and produces output through textboxes. The output and input are stored in a two dimensional 10x6 array. The webpage allows you to create a new sale/ form which is stored in the next array row, view the previous sale/form (which wraps around if you are at the first sale), and view the next sale/form (which wraps around if you are at the last sale/form). My problem is that I don't know how to increment two variables that control where in the array the information is stored, and how I can view the previous/next sales which also wrap around.I am trying to write a webpage that takes input