Question

var el = $(this); // it's a form

At some point:

el.replaceWith('<p>Loading...</p>');

Later:

el.replaceWith(output);

Apparently el doesn’t exist anymore after the first replaceWith…

Can I keep somehow el, obviously with the new content ?

Answer 1

The original el has been removed and replaced by replaceWith. Create a new reference, using the return value of replaceWith:

var el = $(this); // it's a form
el = el.replaceWith('<p>Loading...</p>');
              //`el.replaceWith()` returns the new element
el = el.replaceWith(output);

If you intended to replace the inner content with the new element, while keeping the form, use:

el.html(""); //Clear html
el.append('<p>Loading...</p>');