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Building Interoperable Web Components That Even Work With React

The word "hey" in green.

Those of us who’ve been web developers more than a few years have probably written code using more than one JavaScript framework. With all the choices out there — React, Svelte, Vue, Angular, Solid — it’s all but inevitable. One of the more frustrating things we have to deal with when working across frameworks is re-creating all those low-level UI components: buttons, tabs, dropdowns, etc. What’s particularly frustrating is that we’ll typically have them defined in one framework, say React, but then need to rewrite them if we want to build something in Svelte. Or Vue. Or Solid. And so on.

Wouldn’t it be better if we could define these low-level UI components once, in a framework-agnostic way, and then re-use them between frameworks? Of course it would! And we can; web components are the way. This post will show you how.

As of now, the SSR story for web components is a bit lacking. Declarative shadow DOM (DSD) is how a web component is server-side rendered, but, as of this writing, it’s not integrated with your favorite application frameworks like Next, Remix or SvelteKit. If that’s a requirement for you, be sure to check the latest status of DSD. But otherwise, if SSR isn’t something you’re using, read on.

First, some context

Web Components are essentially HTML elements that you define yourself, like or whatever, from the ground up. They’re covered all over here at CSS-Tricks (including an extensive series by Caleb Williams and one by John Rhea) but we’ll briefly walk through the process. Essentially, you define a JavaScript class, inherit it from HTMLElement, and then define whatever properties, attributes and styles the web component has and, of course, the markup it will ultimately render to your users.

Being able to define custom HTML elements that aren’t bound to any particular component is exciting. But this freedom is also a limitation. Existing independently of any JavaScript framework means you can’t really interact with those JavaScript frameworks. Think of a React component which fetches some data and then renders some other React component, passing along the data. This wouldn’t really work as a web component, since a web component doesn’t know how to render a React component.

Web components particularly excel as leaf components. Leaf components are the last thing to be rendered in a component tree. These are the components which receive some props, and render some UI. These are not the components sitting in the middle of your component tree, passing data along, setting context, etc. — just pure pieces of UI that will look the same, no matter which JavaScript framework is powering the rest of the app.

The web component we’re building

Rather than build something boring (and common), like a button, let’s build something a little bit different. In my last post we looked at using blurry image previews to prevent content reflow, and provide a decent UI for users while our images load. We looked at base64 encoding a blurry, degraded versions of our images, and showing that in our UI while the real image loaded. We also looked at generating incredibly compact, blurry previews using a tool called Blurhash.

That post showed you how to generate those previews and use them in a React project. This post will show you how to use those previews from a web component so they can be used by any JavaScript framework.

But we need to walk before we can run, so we’ll walk through something trivial and silly first to see exactly how web components work.

Everything in this post will build vanilla web components without any tooling. That means the code will have a bit of boilerplate, but should be relatively easy to follow. Tools like Lit or Stencil are designed for building web components and can be used to remove much of this boilerplate. I urge you to check them out! But for this post, I’ll prefer a little more boilerplate in exchange for not having to introduce and teach another dependency.

A simple counter component

Let’s build the classic “Hello World” of JavaScript components: a counter. We’ll render a value, and a button that increments that value. Simple and boring, but it’ll let us look at the simplest possible web component.

In order to build a web component, the first step is to make a JavaScript class, which inherits from HTMLElement:

class Counter extends HTMLElement {}

The last step is to register the web component, but only if we haven’t registered it already:

if (!customElements.get("counter-wc")) {
  customElements.define("counter-wc", Counter);
}

And, of course, render it:

<counter-wc></counter-wc>

And everything in between is us making the web component do whatever we want it to. One common lifecycle method is connectedCallback, which fires when our web component is added to the DOM. We could use that method to render whatever content we’d like. Remember, this is a JS class inheriting from HTMLElement, which means our this value is the web component element itself, with all the normal DOM manipulation methods you already know and love.

At it’s most simple, we could do this:

class Counter extends HTMLElement {
  connectedCallback() {
    this.innerHTML = "<div style='color: green'>Hey</div>";
  }
}

if (!customElements.get("counter-wc")) {
  customElements.define("counter-wc", Counter);
}

…which will work just fine.

Adding real content

Let’s add some useful, interactive content. We need a to hold the current number value and a

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