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    CodeWithSwiz: Privacy-focused embeds for YouTube, Twitter, et al

    Friend, here's a new old experiment πŸ‘‰ regular livecoding. It's like a podcast with video, show notes, regular cadence, and we both learn something new.

    For me it's a regular timebox – Wednesdays 6:30pm Pacific and Sundays 2pm Pacific – to play with new technology, explore ideas, work on open source, and hack.

    For you it's a chance to hear about new libraries and technologies, peek behind the curtain, ask any and all questions you'd like, and with luck see cool things get built.

    Show notes work like a short recap.

    PS: you can read and share this online

    When websites embed 3rd party content like YouTube, Twitter, Facebook, et all, those embeds come with a bunch of cruft. Shitload of JavaScript, heavy code in iframes, and tracking scripts.

    You don't want that.

    Privacy is important and so is performance. A blank page with a single YouTube embed makes 18 requests and loads 2.2 megs of data.

    YouTube embed performance hit
    YouTube embed performance hit

    5 cookies 😳

    cookies from a single YT embed
    cookies from a single YT embed

    What if instead of embedding with an iframe, you showed a thumbnail first? Load dynamic content when user interacts and shows intent. Says "Yes, I wanna see this"

    The way TechLetter.App works for emails. But without taking you to a new page on click.

    Here's the plan:

    • take existing AWS Lambda screenshot machinery
    • make a Gatsby plugin that turns embeds into thumbnails
    • inject vanilla JavaScript to turn into proper embeds

    Started with a dirty proof of concept. It worked 🀘

    Time to build a plugin! That did not go well.

    First, we ran into issues with plugin building for Gatsby. You have to keep clearing cache, rebuilding the whole site, and waiting a lot.

    When your computer is busy streaming, you're waiting a lot.

    Should've written tests instead πŸ˜…

    But fear not, we got the thumbnail part working. First for YouTube, later we can expand. It's a remark plugin like this:

    export default async function (
        { cache, markdownAST },
        pluginOptions: PluginOptions
    ) {
        const transformations = [];
        visit(markdownAST, "link", (linkNode) => {
            const url = linkNode.url as string;
            if (url.match(/^http(s)?:\/\/(www\.)?(youtube\.com|youtu\.be)/)) {
                transformations.push(async () => embed(linkNode, "youtube"));
        await Promise.all(transformations.map((t) => t()));
        return markdownAST;

    Visits all link nodes in your document, checks if they're YouTube, and turns them into a thumbnail embed.

    Transformation to an embed looks like this:

    async function embed(linkNode, embedType: "youtube") {
      const originalUrl = linkNode.url;
      const thumbnailUrl = await getThumbnail(originalUrl);
      if (thumbnailUrl) {
        linkNode.type = "image";
        linkNode.url = thumbnailUrl;
        linkNode.title = "A youtube video";
        linkNode.alt = "A youtube video";
        linkNode.children = null;
        linkNode.data = {
        linkNode.data.hProperties = {
          "data-embed-url": getYouTubeIFrameSrc(originalUrl),
          "data-embed-type": embedType,
      return linkNode;

    linkNode.data.hProperties is how you can add HTML properties to your Markdown nodes. Didn't know that before, stole it from another plugin on stream ✌️

    The getThumbnail method talks to my AWS Lambda running Chrome Puppeteer. Takes a screenshot of the YouTube video, saves it to S3, and returns the URL.

    You can read about that in Serverless Handbook: Chrome puppeteer chapter.

    We're using data-embed-url and data-embed-type to tell the injected JavaScript what to do. Meant to turn this thumbnail into an iframe when you click.

    Gatsby lets us inject JavaScript on page load. Export an onRouteUpdate method from gatsby-browser.js.

    exports.onRouteUpdate = () => {
      if (document.querySelector("[data-embed-url]")) {
    for (let embed of document.querySelectorAll('[data-embed-url]')) {
        embed.addEventListener('click', (event) => {
            const embed = event.currentTarget;
            const type = embed.dataset.embedType;
            const url = embed.dataset.embedUrl;
            const dimensions = embed.getBoundingClientRect();
            if (type === 'youtube') {
                const el = document.createElement('p');
                el.innerHTML = '<iframe title="Youtube embed" width="'+dimensions.width+'px" height="'+dimensions.height+'px" src="'+url+'" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen=""></iframe>';

    Yeah writing code in a string sucks. You don't have React either. And I gotta say vanilla JavaScript has improved lots in the past few years.

    This code looks for all elements with a data-embed-url property and adds a click listener. When you click, it replaces the element with an HTML string.

    Adding it to the page is a matter of injecting a new <script> tag into document head.

    function addJS(jsCode) {
      const s = document.createElement(`script`);
      s.type = `text/javascript`;
      s.innerText = jsCode;

    Where I'm stuck now is with Gatsby shadowing and moving all this code to the existing gatsby-remark-embedder plugin. Got the thumbnails to work, but not the in-browser JavaScript.

    Gatsby shadowing says you can put gatsby-browser.js in your plugin and Gatsby will run that code. But it's not working for me 🀨

    Next time!

    Cheers, ~Swizec

    Published on August 27th, 2020 in CodeWithSwiz, Technical, Markdown, Livecoding

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    Have a burning question that you think I can answer? Hit me up on twitter and I'll do my best.

    Who am I and who do I help? I'm Swizec Teller and I turn coders into engineers with "Raw and honest from the heart!" writing. No bullshit. Real insights into the career and skills of a modern software engineer.

    Want to become a true senior engineer? Take ownership, have autonomy, and be a force multiplier on your team. The Senior Engineer Mindset ebook can help πŸ‘‰ swizec.com/senior-mindset. These are the shifts in mindset that unlocked my career.

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