Uncaught TypeError: Cannot read property 'className' of undefined

Question

The following error is being thrown in Google Chrome\'s developers tools:

Uncaught TypeError: Cannot read property \'className\' of undefined

Answer 1

The other answer put me on the right track.

More succinctly, the error was that the table I was creating was incorrect.

My header columns (inside a thead of course), did not match up with my row columns (inside the tbody)

In my situation, I had too many columns inside the header.