How do I reload a page without a POSTDATA warning in Javascript?

You can't refresh without the warning; refresh instructs the browser to repeat the last action. It is up to the browser to choose whether to warn the user if repeating the last action involves resubmitting data.

You could re-navigate to the same page with a fresh session by doing:

window.location = window.location.href;

Just changing window.location in JavaScript is dangerous because the user could still hit the back button and resubmit the post, which could have unexpected results (such as a duplicate purchase). PRG is a much better solution

Use the Post/Redirect/Get (PRG) pattern

To avoid this problem, many web applications use the PRG pattern — instead of returning an HTML page directly, the POST operation returns a redirection command (using the HTTP 303 response code (sometimes 302) together with the HTTP "Location" response header), instructing the browser to load a different page using an HTTP GET request. The result page can then safely be bookmarked or reloaded without unexpected side effects.

I had some problems with anchor/hash-urls (including #) not reloading using the solution from Rex...

So I finally ended up by removing the hash part:

window.location = window.location.href.split("#")[0];