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

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 the new URL is used?

It would also be nice if the back button would reload the original URL.

I am trying to record JavaScript state in the URL.

If you want it to work in browsers that don't support history.pushState and history.popState yet, the "old" way is to set the fragment identifier, which won't cause a page reload.

The basic idea is to set the window.location.hash property to a value that contains whatever state information you need, then either use the window.onhashchange event, or for older browsers that don't support onhashchange (IE < 8, Firefox < 3.6), periodically check to see if the hash has changed (using setInterval for example) and update the page. You will also need to check the hash value on page load to set up the initial content.

If you're using jQuery there's a hashchange plugin that will use whichever method the browser supports. I'm sure there are plugins for other libraries as well.

One thing to be careful of is colliding with ids on the page, because the browser will scroll to any element with a matching id.

With HTML 5, use the history.pushState function. As an example:

<script type="text/javascript">
var stateObj = { foo: "bar" };
function change_my_url()
{
   history.pushState(stateObj, "page 2", "bar.html");
}
var link = document.getElementById('click');
link.addEventListener('click', change_my_url, false);
</script>

and a href:

<a href="#" id='click'>Click to change url to bar.html</a>

If you want to change the URL without adding an entry to the back button list, use history.replaceState instead.

window.location.href contains the current URL. You can read from it, you can append to it, and you can replace it, which may cause a page reload.

If, as it sounds like, you want to record javascript state in the URL so it can be bookmarked, without reloading the page, append it to the current URL after a # and have a piece of javascript triggered by the onload event parse the current URL to see if it contains saved state.

If you use a ? instead of a #, you will force a reload of the page, but since you will parse the saved state on load this may not actually be a problem; and this will make the forward and back buttons work correctly as well.