Handle URL fragment identifier (anchor) change event in Javascript

How can I write the Javascript callback code that will be executed on any changes in the URL fragment identifier (anchor)?

For example from http://example.com#a to http://example.com#b

Google Custom Search Engines use a timer to check the hash against a previous value, whilst the child iframe on a seperate domain updates the parent's location hash to contain the size of the iframe document's body. When the timer catches the change, the parent can resize the iframe to match that of the body so that scrollbars aren't displayed.

Something like the following achieves the same:

var storedHash = window.location.hash;
window.setInterval(function () {
    if (window.location.hash != storedHash) {
        storedHash = window.location.hash;
        hashChanged(storedHash);
    }
}, 100); // Google uses 100ms intervals I think, might be lower

Google Chrome 5, Safari 5, Opera 10.60, Firefox 3.6 and Internet Explorer 8 all support the hashchange event:

if ("onhashchange" in window) // does the browser support the hashchange event?
    window.onhashchange = function () {
        hashChanged(window.location.hash);
    }

and putting it together:

if ("onhashchange" in window) { // event supported?
    window.onhashchange = function () {
        hashChanged(window.location.hash);
    }
}
else { // event not supported:
    var storedHash = window.location.hash;
    window.setInterval(function () {
        if (window.location.hash != storedHash) {
            storedHash = window.location.hash;
            hashChanged(storedHash);
        }
    }, 100);
}

jQuery also has a plugin that will check for the hashchange event and provide its own if necessary - http://benalman.com/projects/jquery-hashchange-plugin/.

EDIT: Updated browser support (again).

An event listener can be added for the hashchange event, which will fire whenever the fragment identifier changes:

window.addEventListener('hashchange', function() {
  // Perform action
  // [...]
})

I would recommend this approach instead of overwriting window.onhashchange, otherwise you will block the event for other plugins.

Looking at the global browser usage today, a fallback is longer needed, as modern browsers support this event.

From what I see in other SO questions, the only workable cross-browser solution is a timer. Check out this question for example.

setInterval() is only universal solution for now. But there are some light in the future in form of hashchange event

(Just for the record.) The YUI3 "hashchange" synthetic event does more or less the same thing as the accepted answer

YUI().use('history-hash', function (Y) {
  Y.on('hashchange', function (e) {
    // Handle hashchange events on the current window.
  }, Y.config.win);
});

Here's a simple way that worked just fine for me with jQuery. I've added a animation to scroll to the anchor element aswell:

$(window).on('hashchange', function(e){
     var origEvent = e.originalEvent;
		 var elementToBeClicked = $('a[href^="'+window.location.hash+'"]').click();  
		$([document.documentElement, document.body]).animate({
        scrollTop: 200
    }, 100);
});

Hope it works for you.

You can get more info from this

Mutation event types

> The mutation event module is designed > to allow notification of any changes > to the structure of a document, > including attr and text modifications.