Long gone are the days when Internet Explorer had 95% of the browser market. We have lived in multi-browser world since the start of the web. Whilst this has its plus point, it also has its downsides – none more so than ensuring backwards compatibility.
Using HTML5 today is not simply a case of does the browser support it or not, but what aspects of the huge specification does it support and to what extent. A good site for seeing the various levels of support across browser releases, against different areas of the HTML5 specification can be found at CanIUse.com.
The W3C’s answer to developers creating solutions with HTML5 is that the new features of the spec should “gracefully degrade” when used in older browsers. Essentially this means the new markup or API is ignored and doesn’t cause the page to crash. Developers should test and develop backwards compatibility. This can be an onerous task. However help is at hand with libraries like Modernizr you can detect what features of HTML5 the browser supports.
Once you know that the browser doesn’t support a HTML5 feature you have used you can write or use a 3rd party “polyfill”. In HTML, a polyfill is essentially code that is used to provide alternative behaviour to simulate HTML5 features in a browser that does not support that particular feature. There are lots of sites providing polyfills for different parts of the HTML5 spec, a pretty good one can be found here it lists lots of libraries covering almost all parts of the specification.
For me a big concern is that I’ve not yet been able to find a single provider that gives you polyfills for the whole of HTML5, or even the majority of the specification. This could mean that you have to use several different libraries, which may or may not be compatible with each other. Another big concern is that each polyfill will provide varying levels of browser backwards compatibility i.e. some will support back to IE 6 and some not.
With users moving more of their browsing towards smartphones and tablets which typically have the latest browser technology supporting HTML5, backwards compatibility may not be an issue. However it will be several years before the HTML5 spec is complete, and even then there are new spec’s being created all the time within the W3C. So far from being a temporary fix the use of polyfills will become a standard practice in web development, unless of course you take the brave stance of saying your application is only supported on HTML5 browsers.
However this does raise another question, if you can simulate HTML5 behaviour do you need to start using HTML5 at all to create richer applications? The answer is quite possibly not, but having one will certainly improve your user experience and make development of your rich internet applications simpler.