Progressive Enhancement
The subtle difference between progressive enhancement and graceful degradation is lost on too many. Many of those that support “mobile first” don’t support progressive enhancement, which is an oxymoron.
Mobile first is progressive enhancement. Start with the most important part of any site: content. Mark it up. Semantically. Why? Because some readers experience your site without CSS. It’s true. Some just want the content. Screenreaders and search engines are the largest of these.
Then style the content. That’s the CSS. Mobile first says start with the LCD, the Lowest Common Denominator: mobile. But make sure that your CSS works in the LCD. That might be IE 9. It might be IE 11. Look at your analytics if possible. Progressive enhancement means add features when available. Progressively enhancing. You see? So if you are using a feature that is only available to IE 11 and better (Chrome, Firefox, etc.) and you need to support IE 9, make sure that the feature is not necessary for the user experience.
Then JavaScript. Understand that some have JavaScript disabled. Whether it be over-cautious IT departments, search engines that cannot handle rendering and parsing JavaScript, users with bad network connectivity that fails to load it, or most importantly screenreaders that help those with handicaps consume the content of the web. JavaScript is an enhancement. So long as you have the last two components set, your page works fine when JS is turned off. So, as features are available, use them.
But see, too many developers these days have abandoned this methodology that fueled the Web Standards movement. Instead, sites require over 300 kilobytes of JavaScript libraries and don’t load anything if JavaScript is disabled. Instead of starting with content, they start with jQuery, Angular, React, or whatever the library de jour is. Everything is built in JavaScript. This is graceful degradation, start with the Greatest Common Denominator. Except many aren’t even testing for the LCD. They aren’t turning off JS to make sure that their site will work for those that disable JS. Often they even break the most basic components of the web browser: the URL and the back/forward buttons.
We need to get back to progressive enhancement as the standard. We need to get back to the promise that the web is accessible to all, no matter the device they use.