It's been a week or two since I've played with web components, and this morning I was thinking about them (because that's just how cool I am) and comparing and contrasting them with Eleventy's WebC support. I think WebC is incredibly compelling, and honestly, if I knew I were deploying to Jamstack, I'd probably always pick that over "vanilla" web components. Using WebC lets me do quite a bit on the server, and in my build, and reduces the amount of JavaScript sent to the client. That's always a good thing (usually), but I can also see people using regular web components with Eleventy as well. I'm still very new to all of this and still figuring out what makes sense where, but I thought it would be kind of fun to build the same component in both and compare and contrast the result.

For my component, I decided to build a lazy-loading YouTube embed. Basically, it would default to an image thumbnail of the video (there's a standard URL format where if you know the ID of a video, you can get multiple different thumbnails) and only load the "full" YouTube embed experience after clicking.

I found an excellent example of this by Arthur Corenzan way back in 2019, Lazy load embedded YouTube videos. In his post, he describes how he used the srcdoc attribute of iframe. Now, I don't claim to know every HTML tag and attribute out there, but I feel like I've got a pretty good handle on the platform, and I've got to say, that was a new one for me.

srcdoc lets you specify the content of an iframe instead of using a URL. So for example:

    srcdoc="<img src=''>"></iframe>

You can see this in play here:

See the Pen srcdoc example by Raymond Camden (@cfjedimaster) on CodePen.

So his technique makes use of this. His example looks like so (with extra stuff removed):

  srcdoc="<a href=><img src=></a>">

Cool, so let's take this basic idea and turn it into a web component first.

The Web Component Version #

My web component code takes his template code and looks for arguments for height, width, videoid, and title. Here's the entire component:

class YoutubeEmbed extends HTMLElement {

    constructor() {


        const shadow = this.attachShadow({mode:'open'});

        this.width = 560;
        this.height = 315;
        this.title = '';
        this.videoid = null;

        if(this.hasAttribute('width')) this.width = parseInt(this.getAttribute('width'), 10);
        if(this.hasAttribute('height')) this.height = parseInt(this.getAttribute('height'), 10);
        if(this.hasAttribute('title')) this.title = this.getAttribute('title');
        if(this.hasAttribute('videoid')) {
            this.videoid = this.getAttribute('videoid');
        } else {
            console.warn('No videoid passed to youtube-embed tag, aborting.');

        const div = document.createElement('div');
        div.innerHTML = `
  srcdoc="<style>*{padding:0;margin:0;overflow:hidden}html,body{height:100%}img,span{position:absolute;width:100%;top:0;bottom:0;margin:auto}span{height:1.5em;text-align:center;font:48px/1.5 sans-serif;color:white;text-shadow:0 0 0.5em black}</style><a href=${this.videoid}?autoplay=1><img src=${this.videoid}/hqdefault.jpg alt='${this.title}' title='${this.title}'><span>▶</span></a>"
  allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture"


customElements.define('youtube-embed', YoutubeEmbed);

There really isn't much to it. The only real logic is when I define innerHTML and use the attributes passed in. This is exposed as youtube-embed which means it can be used like so:

<youtube-embed videoid="a5C4_FZ3s-k" title="Presentation on Alpine"></youtube-embed>
<script src="youtube-embed.js"></script>

And it just plain works! For the most part. If you read the comments on his blog post, you'll note folks mentioning that the video won't play on click, despite the autoplay parameter. I can confirm this behavior. As someone who was railed against autoplay videos for over a decade, the browser working against autoplay is something I can get behind. I think one could consider a modification of the component such that instead of a play button, it perhaps has text saying "Click here to load" or some such, so the expectation is set that it's one click to load, another to play.

To me though, the real benefit comes in when you look at the difference in what's being loaded. On a page where I use this component, the initial is right below 2.5kb. When you click to load the video, that goes to nearly a meg. That's a huge difference and we're saving all of that from the user's first load which is a great thing.

You can demo this version here:

See the Pen youtube-embed by Raymond Camden (@cfjedimaster) on CodePen.

And the source may be found here too:

Now, let's look at the WebC version.

The WebC Component Version #

Honestly, I don't know if "WebC Component" makes sense as it's got the C in the name already. I'm probably overthinking it, but let me know what you think. Ok, let's talk Eleventy and WebC. First off, if you haven't read the WebC docs yet, please do. And if you need a little extra help, my introduction may help. I've got a small Eleventy site with the WebC plugin installed, configured to look at "_includes/components/**/*.webc for components. I built a new Liquid page and used the same code to call my component:

<youtube-embed videoid="a5C4_FZ3s-k" title="Presentation on Alpine"></youtube-embed>

And actually, that's a lie. It isn't the same code, do you see what's missing? The script source. It's completely unnecessary now as Eleventy's going to handle all of that in the build process. For my actual component, here is youtube-embed.webc:

<template webc:type="11ty" 11ty:type="liquid">
{% if width == blank %}
    {% assign width = "560" %}
{% endif %}
{% if height == blank %}
    {% assign height = "315" %}
{% endif %}

  width="{{ width }}"
  height="{{ height }}"
  srcdoc="<style>*{padding:0;margin:0;overflow:hidden}html,body{height:100%}img,span{position:absolute;width:100%;top:0;bottom:0;margin:auto}span{height:1.5em;text-align:center;font:48px/1.5 sans-serif;color:white;text-shadow:0 0 0.5em black}</style><a href={{videoid}}?autoplay=1><img src={{videoid}}/hqdefault.jpg alt='{{title}}' title='{{title}}'><span>▶</span></a>"
  allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture"


This is just a Liquid template with a bit of logic on top, and then just dynamic output. I'm not a fan of needing to wrap the entire thing in template tags so I can use Liquid, but I can get over it too.

For such a simple test, the size savings wasn't really big. I believe it was 1k less than the "vanilla" WebC version, but this one works without JavaScript, and any easy saving is a good saving!

While I don't have this demo running anywhere, you can find it (and other things I was playing with) here: As always, don't forget this is a new feature, I'm learning, and it's bound to change before release.