Re-fill form fields when toggling Javascript

[lypwig]

When the user clicks on the no-JS button, the page reloads without keeping the current fields content.

This data lost can be annoying: suppose that the user writes a long markdown text in a text-area, then clicks on a preview button that renders the markdown on the client-side. It will not work since JS is disabled, so the user enabled JS, but at this moment he/she will lost all the form content.

It could be practical to fill all the form inputs by their previous value when reloading the page.