Change the URL in the browser without loading the new page using JavaScript

Question

How would I have a JavaScript action that may have some effects on the current page but would also change the URL in the browser so if the user hits reload or bookmark, then

Answer 1

Facebook's photo gallery does this using a #hash in the URL. Here are some example URLs:

Before clicking 'next':

/photo.php?fbid=496429237507&set=a.218088072507.133423.681812507&pid=5887027&id=681812507

After clicking 'next':

/photo.php?fbid=496429237507&set=a.218088072507.133423.681812507&pid=5887027&id=681812507#!/photo.php?fbid=496435457507&set=a.218088072507.133423.681812507&pid=5887085&id=681812507

Note the hash-bang (#!) immediately followed by the new URL.