Question

$("a.avatar").click(function(e){
      e.preventDefault();
      $("#thumbnails").fadeIn();
    });

and

$("a.avatar").click(function(e){
      $("#thumbnails").fadeIn();
          return false;
    });

Both can achieve the same goal for me.

Answer 1

Returning false from jQuery event handlers is equivalent to calling both, e.preventDefault and e.stopPropagation.

So the difference is that preventDefault will only prevent the default event action to occur, i.e. a page redirect on a link click, a form submission, etc. and return false will also stop the event flow.