Using JS to provide the front-end layout is not ideal

The idea is neat, but I think using JS on the front-end is a bit overkill and bad for the UX. The layout is created on when the document finishes loading, so with a bad network or a heavy content on the page it looks jumpy.

I’d use a specific class on the wrapper element, like first-col-XXX, where the XXX is the width of the first column. And then I’d use CSS to style the first child, like flex-basis: XXX and so on..