> The pro-web-component folks argue that WCs are standardised and will continue to work basically indefinitely regardless of the ebbs and flows of popular libraries, and because it's easier to progressively enhance and therefore more accessible. This is correct, and those points are valuable if what you seek is a way to add resilient islands of interactivity to your document.

I'm not sure that's even that correct. If you write code using browser APIs that are currently standardised, your code will work indefinitely, whether or not you use Web Components, React, or jQuery. Hell, we used to have jQuery-based components with the whole $(...).datepicker() system. Yes, it has its flaws, but it'll still work today if that's what your want from it.

Secondly, I don't think Web Components do work well from a progressive enhancement perspective. Progressive enhancement is starting from the bare minimum (i.e. just HTML and some styles, if that), and progressively adding features to that initial state that don't prevent any of the previously-added features from working. So you start with an HTML form skeleton, and you add some validation attributes, you add an event handler that calls fetch instead of reloading the page, you extend the address input so that it suggests real addresses - but the whole time, the HTML form is still there and it still works.

But without Javascript, Web Components are essentially empty holes that can't do anything. They don't progressively enhance anything. You can to a certain extent wrap existing elements, you can take the isomorphic approach described in this post, etc. But even when you do that, the browser will replace the contents of the element with the component's rendered output when the Javascript comes online, potentially deleting any user inputs if they'd interacted with the previous context. If your aim is true progressive enhancement, you should probably look in a different direction.

In fairness, I don't disagree that these claims are often made by Web Component proponents. But I think they're the wrong claims to be making. Web Components seem to be most useful if you're trying to isolate a complex stateful component written by one person or team and ended it into a complex stressful application written by a different person or team. They're essentially like lightweight iframes. This is really useful, and should be promoted more - but it's also quite a specific use.