SOFT6008 CheckSum Tips

Don't go messing with buttons and functions. Doing so will make your code very hard to debug.

Start with a prompt and output the input with a document.write
After each step of the processing output the new information using document.write
When the code is working, and you have tested it thoroughly, you can remove the document.writes and swap the code up in a function. You can then plug that function into a page with buttons and DOM modifications.