TL;DR
Let’s say that your web application has an import feature. You would like application users to use an Excel-like application to insert or copy/paste data to import it into your application.
jExcel
One way to do it is with the jExcel javascript library. Here is an example where you create a table using hardcoded values. jExcel is an interactive spreadsheet, which means you can add rows and columns. But in the import data table, you already defined supported columns, and you would like to forbid users to interactively add using TAB new columns. More confusion is created because those columns are automatically named with English alphabet letters, like in Excel (A, B, C, …).
Here is a code snippet where you forbid adding columns with TAB keystroke:
