An update (March 2016) on the current state & recommendations for JavaScript …

The end of responsive images - Piccalilli

Hallelujah! Support for sizes="auto" is finally landing in Firefox and Safari! Praise be!

HTML Video Poster Image: Enable Responsive Images and ALT Text for Poster by allowing a child IMG Element (with an optional Picture Element wrapper) to Control the Video Poster Image · Issue #10378 · whatwg/html

This is such a brilliant idea! Why not allow an img element inside video element in order to provide a responsive, accessible poster image?

Alistair Davidson / validation-enhancer · GitLab

Here’s another nice progressive web component for your forms, this time for showing error messages.

Never Lose Form Progress Again :: Aaron Gustafson

Here’s an excellent progressive web component from Aaron—wrap a custom element around your exising form and your good to go:

At its core, form-saver is a small web component that wraps a form, keeps an eye on it, stores values in localStorage, and restores them when the page loads again. Better yet, it clears out saved data after a successful submission so you’re not accidentally resurrecting stale information the next time someone stops by.

Don’t judge a book by its cover

Some neat CSS from Tess that’s a great example of progressive enhancement; these book covers look good in all browsers, but they look even better in some.