Can I use non existing CSS classes?

Answer 1

As is mentioned by so many others, yes, using classes with no assigned CSS is perfectly valid and rather than thinking of them as 'CSS classes' you should simply recognise the semantics of class and ID to be groups and individual elements respectively.

I wanted to chip in as I felt an important point hasn't been raised given the example. If you ever need to do visual manipulations to a variable length of elements (in this case you're using table rows) then it always makes sense to recognise that the cost of doing so through Javascript could potentially be very expensive (e.g if you have thousands of rows).

In this situation let's say we know that column 2 always has the potential to be hidden (it's a conscious function of your table) then it makes sense to design a CSS style to handle this use case.

table.target-hidden .target { display: none; }

Then rather than using JS to traverse through the DOM finding N elements we simply need to toggle a class on one (our table).

$("table").addClass("target-hidden")

By assigning the table an ID this would be even quicker and you could even just refer to the column by using the :nth-child selector which would reduce your markup further but I can't comment on efficiency. Another reason for doing this is that I hate inline styling, and will go to great lengths to eradicate it!