This is one of the possible ways:
Please look at the onSubmit attribute of form:
http://www.htmlcodetutorial.com/forms/_FORM_onSubmit.html[
^].
Note that this is the Javascript code which is called
before actual submission and it defines if the submission happens or not. So, if it returns true, submission starts. So, you can show some indicator in this function. You can just show some message or start some Javascript animation. Now, let's assume that the form
action
attribute points to the same URL of the current page (always a good idea). So, when the page is rendered, the user will see the content without this indicator. Based on this idea, you can implement different effect except… showing the percentage of loaded content; but there is not a reason to be sorry about it: this time is pretty much unpredictable anyway.
—SA