Hate to be a negative Nancy, but on a bog standard Chrome on a bog standard Windows 10, in the first exercise the HJKL keys do nothing. The arrow keys do work...
noremap <Up> <Nop>
noremap <Down> <Nop>
noremap <Left> <Nop>
noremap <Right> <Nop>
There, now your arrow keys do nothing, too! (This is a good way to "train" yourself to not depend on the arrow keys.)