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

Progressive enhancement brings everyone in - The History of the Web

This is a great history of the idea of progressive enhancement:

It is an idea that has been lasting and enduring for two decades, and will continue.

You can use Web Components without the shadow DOM

So what are the advantages of the Custom Elements API if you’re not going to use the Shadow DOM alongside it?

1. Obvious Markup
2. Instantiation is More Consistent
3. They’re Progressive Enhancement Friendly

Request for developer feedback: customizable select  |  Blog  |  Chrome for Developers

I’m very glad to see that work has moved away from a separate selectmenu element to instead enhancing the existing select element—I could never see an upgrade path for selectmenu, but now there are plenty of opportunities for progressive enhancement.

HTML Web Components Can Have a Little Shadow DOM, As A Treat | Scott Jehl, Web Designer/Developer

This is an interesting thought from Scott: using Shadow DOM in HTML web components but only as a way of providing sort-of user-agent styles:

providing some default, low-specificity styles for our slotted light-dom HTML elements while allowing them to be easily overridden.

Futuristic Progressive Enhancement - Jim Nielsen’s Blog

We’re all tired of: write some code, come back to it in six months, try to make it do more, and find the whole project is broken until you upgrade everything.

Progressive enhancement allows you to do the opposite: write some code, come back to it in six months, and it’s doing more than the day you wrote it!