I assume you mean something like Google Doc's spreadsheet app. Let's say it's 1996.

The DOM wasn't standard, HTML4 was still in the works. I'm not sure if IE2/3 or Netscape 2 could even dynamically access table elements at the time.

Javascript performance was utterly terrible, and JScript had a strong presence that created an important and problematic language/support divide.

CSS didn't exist at all, your visual styles were either images or elements rendered as the browser saw fit.

XHR didn't exist and wouldn't exist until IE5, 4 years later. There was no way to update a page without a round trip to the server. This was also during the days of AOL and Dialup.