Modern HTML5 Techniques for changing classes
Modern browsers have added classList which provides methods to make it easier to manipulate classes without needing a library:
document.getElementById("MyElement").classList.add('MyClass');
document.getElementById("MyElement").classList.remove('MyClass');
if ( document.getElementById("MyElement").classList.contains('MyClass') )
document.getElementById("MyElement").classList.toggle('MyClass');
Unfortunately, these do not work in Internet Explorer prior to v10, though there is a shim to add support for it to IE8 and IE9, available from this page. It is, though, getting more and more supported.
Simple cross-browser solution
The standard JavaScript way to select an element is using document.getElementById("Id")
, which is what the following examples use - you can of course obtain elements in other ways, and in the right situation may simply use this
instead - however, going into detail on this is beyond the scope of the answer.
To change all classes for an element:
To replace all existing classes with one or more new classes, set the className attribute:
document.getElementById("MyElement").className = "MyClass";
(You can use a space-delimited list to apply multiple classes.)
To add an additional class to an element:
To add a class to an element, without removing/affecting existing values, append a space and the new classname, like so:
document.getElementById("MyElement").className += " MyClass";
To remove a class from an element:
To remove a single class to an element, without affecting other potential classes, a simple regex replace is required:
document.getElementById("MyElement").className =
document.getElementById("MyElement").className.replace
( /(?:^|\s)MyClass(?!\S)/g , '' )
/* Code wrapped for readability - above is all one statement */
An explanation of this regex is as follows:
(?:^|\s) # Match the start of the string or any single whitespace character
MyClass # The literal text for the classname to remove
(?!\S) # Negative lookahead to verify the above is the whole classname
# Ensures there is no non-space character following
# (i.e. must be the end of the string or space)
The g
flag tells the replace to repeat as required, in case the class name has been added multiple times.
To check if a class is already applied to an element:
The same regex used above for removing a class can also be used as a check as to whether a particular class exists:
if ( document.getElementById("MyElement").className.match(/(?:^|\s)MyClass(?!\S)/) )
### Assigning these actions to onclick events:
Whilst it is possible to write JavaScript directly inside the HTML event attributes (such as onclick="this.className+=' MyClass'"
) this is not recommended behaviour. Especially on larger applications, more maintainable code is achieved by separating HTML markup from JavaScript interaction logic.
The first step to achieving this is by creating a function, and calling the function in the onclick attribute, for example:
<script type="text/javascript">
function changeClass(){
// Code examples from above
}
</script>
...
<button onclick="changeClass()">My Button</button>
(It is not required to have this code in script tags, this is simply for the brevity of example, and including the JavaScript in a distinct file may be more appropriate.)
The second step is to move the onclick event out of the HTML and into JavaScript, for example using addEventListener
<script type="text/javascript">
function changeClass(){
// Code examples from above
}
window.onload = function(){
document.getElementById("MyElement").addEventListener( 'click', changeClass);
}
</script>
...
<button id="MyElement">My Button</button>
(Note that the window.onload part is required so that the contents of that function are executed after the HTML has finished loading - without this, the MyElement might not exist when the JavaScript code is called, so that line would fail.)
JavaScript Frameworks and Libraries
The above code is all in standard JavaScript, however, it is common practice to use either a framework or a library to simplify common tasks, as well as benefit from fixed bugs and edge cases that you might not think of when writing your code.
Whilst some people consider it overkill to add a ~50 KB framework for simply changing a class, if you are doing any substantial amount of JavaScript work or anything that might have unusual cross-browser behavior, it is well worth considering.
(Very roughly, a library is a set of tools designed for a specific task, whilst a framework generally contains multiple libraries and performs a complete set of duties.)
The examples above have been reproduced below using jQuery, probably the most commonly used JavaScript library (though there are others worth investigating too).
(Note that $
here is the jQuery object.)
Changing Classes with jQuery:
$('#MyElement').addClass('MyClass');
$('#MyElement').removeClass('MyClass');
if ( $('#MyElement').hasClass('MyClass') )
In addition, jQuery provides a shortcut for adding a class if it doesn't apply, or removing a class that does:
$('#MyElement').toggleClass('MyClass');
### Assigning a function to a click event with jQuery:
$('#MyElement').click(changeClass);
or, without needing an id:
$(':button:contains(My Button)').click(changeClass);
Best Answer
Use PushState and Precomposition
The current (2015) way to do this is using the JavaScript pushState method.
PushState changes the URL in the top browser bar without reloading the page. Say you have a page containing tabs. The tabs hide and show content, and the content is inserted dynamically, either using AJAX or by simply setting display:none and display:block to hide and show the correct tab content.
When the tabs are clicked, use pushState to update the url in the address bar. When the page is rendered, use the value in the address bar to determine which tab to show. Angular routing will do this for you automatically.
Precomposition
There are two ways to hit a PushState Single Page App (SPA)
The initial hit on the site will involve hitting the URL directly. Subsequent hits will simply AJAX in content as the PushState updates the URL.
Crawlers harvest links from a page then add them to a queue for later processing. This means that for a crawler, every hit on the server is a direct hit, they don't navigate via Pushstate.
Precomposition bundles the initial payload into the first response from the server, possibly as a JSON object. This allows the Search Engine to render the page without executing the AJAX call.
There is some evidence to suggest that Google might not execute AJAX requests. More on this here:
https://web.archive.org/web/20160318211223/http://www.analog-ni.co/precomposing-a-spa-may-become-the-holy-grail-to-seo
Search Engines can read and execute JavaScript
Google has been able to parse JavaScript for some time now, it's why they originally developed Chrome, to act as a full featured headless browser for the Google spider. If a link has a valid href attribute, the new URL can be indexed. There's nothing more to do.
If clicking a link in addition triggers a pushState call, the site can be navigated by the user via PushState.
Search Engine Support for PushState URLs
PushState is currently supported by Google and Bing.
Google
Here's Matt Cutts responding to Paul Irish's question about PushState for SEO:
http://youtu.be/yiAF9VdvRPw
Here is Google announcing full JavaScript support for the spider:
http://googlewebmastercentral.blogspot.de/2014/05/understanding-web-pages-better.html
The upshot is that Google supports PushState and will index PushState URLs.
See also Google webmaster tools' fetch as Googlebot. You will see your JavaScript (including Angular) is executed.
Bing
Here is Bing's announcement of support for pretty PushState URLs dated March 2013:
http://blogs.bing.com/webmaster/2013/03/21/search-engine-optimization-best-practices-for-ajax-urls/
Don't use HashBangs #!
Hashbang urls were an ugly stopgap requiring the developer to provide a pre-rendered version of the site at a special location. They still work, but you don't need to use them.
Hashbang URLs look like this:
domain.com/#!path/to/resource
This would be paired with a metatag like this:
<meta name="fragment" content="!">
Google will not index them in this form, but will instead pull a static version of the site from the _escaped_fragments_ URL and index that.
Pushstate URLs look like any ordinary URL:
domain.com/path/to/resource
The difference is that Angular handles them for you by intercepting the change to document.location dealing with it in JavaScript.
If you want to use PushState URLs (and you probably do) take out all the old hash style URLs and metatags and simply enable HTML5 mode in your config block.
Testing your site
Google Webmaster tools now contains a tool which will allow you to fetch a URL as google, and render JavaScript as Google renders it.
https://www.google.com/webmasters/tools/googlebot-fetch
Generating PushState URLs in Angular
To generate real URLs in Angular, rather than # prefixed ones, set HTML5 mode on your $locationProvider object.
Server Side
Since you are using real URLs, you will need to ensure the same template (plus some precomposed content) gets shipped by your server for all valid URLs. How you do this will vary depending on your server architecture.
Sitemap
Your app may use unusual forms of navigation, for example hover or scroll. To ensure Google is able to drive your app, I would probably suggest creating a sitemap, a simple list of all the urls your app responds to. You can place this at the default location (/sitemap or /sitemap.xml), or tell Google about it using webmaster tools.
It's a good idea to have a sitemap anyway.
Browser support
Pushstate works in IE10. In older browsers, Angular will automatically fall back to hash style URLs
A demo page
The following content is rendered using a pushstate URL with precomposition:
http://html5.gingerhost.com/london
As can be verified, at this link, the content is indexed and is appearing in Google.
Serving 404 and 301 Header status codes
Because the search engine will always hit your server for every request, you can serve header status codes from your server and expect Google to see them.