The currently agreed best practice is to detect if a feature is supported and gracefully degrade if it isn’t. Do this on a feature by feature bases so that user

The currently agreed best practice is to detect if a feature is supported and gracefully degrade if it isn’t. Do this on a feature by feature bases so that users gradually get better experience as they upgrade their browsers. However, as other comments have pointed out, feature detection is not always optimal—or even possible—so a whitelist is sometimes needed. This is where YouTube fails. It wrongly doesn’t add the new Chromium based Edge browser to their whitelist. And even then the site doesn’t progressively enhance as it detects supported features.