Quick proof of concept, srcset polyfill

This is only showing a potential polyfill for srcset attribute on img. It's only a quick proof of concept.

The minimum (and useful) code that should have a reasonable fallback story is:

<img style="display:none"
    srcset="small.png 500w,
            big.png">
<noscript><img src="small.png" alt="Alt here"></noscript>

Only set alt on the img in <noscript>, it'll be copied by the javascript out (if not, you'll get two alt texts if you have no javascript).

style for Internet Explorer, it shows a broken image icon without (you may be okay with that, and can remove style if so).

Test

View source to see the hacky javascript (which you could write into a nice polyfill).