On – window.location.hash – Change?

On – window.location.hash – Change?

I am using Ajax and hash for navigation.
Is there a way to check if the window.location.hash changed like this?
http://example.com/blah#123 to http://example.com/blah#456
It works if I check it when the document loads.
But if I have #hash based navigation it doesn’t work when I press the back button on the browser (so I jump from blah#456 to blah#123).
It shows inside the address box, but I can’t catch it with JavaScript.

Solutions/Answers:

Solution 1:

The only way to really do this (and is how the ‘reallysimplehistory’ does this), is by setting an interval that keeps checking the current hash, and comparing it against what it was before, we do this and let subscribers subscribe to a changed event that we fire if the hash changes.. its not perfect but browsers really don’t support this event natively.


Update to keep this answer fresh:

If you are using jQuery (which today should be somewhat foundational for most) then a nice solution is to use the abstraction that jQuery gives you by using its events system to listen to hashchange events on the window object.

$(window).on('hashchange', function() {
  //.. work ..
});

The nice thing here is you can write code that doesn’t need to even worry about hashchange support, however you DO need to do some magic, in form of a somewhat lesser known jQuery feature jQuery special events.

With this feature you essentially get to run some setup code for any event, the first time somebody attempts to use the event in any way (such as binding to the event).

In this setup code you can check for native browser support and if the browser doesn’t natively implement this, you can setup a single timer to poll for changes, and trigger the jQuery event.

This completely unbinds your code from needing to understand this support problem, the implementation of a special event of this kind is trivial (to get a simple 98% working version), but why do that when somebody else has already.

Solution 2:

HTML5 specifies a hashchange event. This event is now supported by all modern browsers. Support was added in the following browser versions:

  • Internet Explorer 8
  • Firefox 3.6
  • Chrome 5
  • Safari 5
  • Opera 10.6

Solution 3:

Note that in case of Internet Explorer 7 and Internet Explorer 9 the if statment will give true (for “onhashchange” in windows), but the window.onhashchange will never fire, so it’s better to store hash and check it after every 100 millisecond whether it’s changed or not for all versions of Internet Explorer.

    if (("onhashchange" in window) && !($.browser.msie)) {
         window.onhashchange = function () {
              alert(window.location.hash);
         }
         // Or $(window).bind( 'hashchange',function(e) {
         //       alert(window.location.hash);
         //   });
    }
    else {
        var prevHash = window.location.hash;
        window.setInterval(function () {
           if (window.location.hash != prevHash) {
              prevHash = window.location.hash;
              alert(window.location.hash);
           }
        }, 100);
    }

EDIT –
Since jQuery 1.9, $.browser.msie is not supported. Source: http://api.jquery.com/jquery.browser/

Solution 4:

There are a lot of tricks to deal with History and window.location.hash in IE browsers:

  • As original question said, if you go from page a.html#b to a.html#c, and then hit the back button, the browser doesn’t know that page has changed. Let me say it with an example: window.location.href will be ‘a.html#c’, no matter if you are in a.html#b or a.html#c.

  • Actually, a.html#b and a.html#c are stored in history only if elements ‘<a name=”#b”>’ and ‘<a name=”#c”>’ exists previously in the page.

  • However, if you put an iframe inside a page, navigate from a.html#b to a.html#c in that iframe and then hit the back button, iframe.contentWindow.document.location.href changes as expected.

  • If you use ‘document.domain=something‘ in your code, then you can’t access to iframe.contentWindow.document.open()’ (and many History Managers does that)

I know this isn’t a real response, but maybe IE-History notes are useful to somebody.

Solution 5:

Firefox has had an onhashchange event since 3.6. See window.onhashchange.

Solution 6:

Ben Alman has a great jQuery plugin for dealing with this: http://benalman.com/projects/jquery-hashchange-plugin/

If you’re not using jQuery it may be an interesting reference to dissect.