Including one centralised banner to a complete portfolio of internet sites through the ability of ‘the sting’

Should you work for a UK organisation or firm in an internet/digital function, you’ve got most likely spent at the very least a while within the final week including a banner to considered one of your websites referencing the Queen’s demise and the way terribly unhappy your employer is about it.

Should you reside elsewhere on the planet then perhaps you’ve got labored on an analogous banner however regarding Covid, Russia’s battle towards Ukraine, or the homicide of George Floyd and the BLM motion. Should you work in a metropolis centre for a really massive firm, your employer might have a plan for responding to an act of terrorism that includes pushing quickly altering messages to your web site. On the lighter facet of issues, you might have been requested to rapidly add a banner to rejoice one thing joyous, reminiscent of a well-deserved prize win.

In my earlier job, we did a brisk commerce at the beginning of Covid in including zero-deployment banners to shopper websites utilizing Google Tag Supervisor to inject JavaScript markup into their pages, however this method causes format shift and is sluggish. On this article, we’ll have a look at a far superior method made potential by trendy CDNs and suppliers like AWS, Cloudflare, Fastly, Akamai, and Netlify.

Responding to an emergency in a unified means throughout a complete property of company web sites

When 💩 hits the fan it is essential to current a unified entrance and to make info accessible in all places as quickly as it’s prepared, however with out the overhead and threat of human error that comes from making an attempt to coordinate too many groups. Plus, your product homeowners, supply managers, builders, and everybody else most likely have extra beneficial issues to be doing than cascading content material modifications and babysitting manufacturing releases to tweak the textual content of a banner that lots of your clients will find yourself ignoring (he says, not talking from private expertise – trustworthy!)

Think about working in a big firm and needing so as to add your message of celebration, hazard, or woe to the entire property or portfolio of various web sites, together with a advertising and marketing website, an e-commerce website, the corporate weblog, a jobs website, an intranet, and so forth. Or working in a gaggle of firms, like how the Co-op (my employer) has a web site for our meals/comfort retailer enterprise, an ecommerce web site for our meals enterprise, a web site for our authorized companies enterprise, insurance coverage enterprise, funeralcare enterprise, plus for our membership proposition, and so forth. That is lots of totally different web sites so as to add our banner to!

Time could be of the essence, and in an emergency or one more ‘unprecedented’ state of affairs there could be no time for confusion, so we would not need the person product groups that personal all these websites to should handle the content material and launch the modifications.

It would not be too onerous to have a single place delivering the message banner content material (a centrally managed CMS), however it’s more durable to inject the HTML, JavaScript, and CSS into a set of various websites directly with out requiring a bunch of various methods to be up to date and deployment/launch processes to be kicked off individually.

How can a world piece of content material be added frictionlessly to a number of websites?

For a demo, I used a Netlify edge operate to make an instance endpoint (supply) at that returns considered one of 3 potential messages:

const imagineTheseCameFromACMS = [
    theme: THEMES.emergency,
    text: " bad has happened, but all our staff are safe. We are posting hourly updates on our Twitter page.",
    link: "",
    theme: THEMES.sombre,
    text: " are saddened by X and wish Y",
    theme: THEMES.celebratory,
    text: `We won best place to work ${new Date().getFullYear()}!!!11`,
    link: "",
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Because the code says, think about this endpoint comes from a CMS like Contentful, Drupal, WordPress and many others and is managed by a central comms crew who is aware of to solely use it when one thing has occurred that’s both very particular (yay!), very horrible (eeek…), or very important-in-the-eyes-of-PR (no remark 💂).

I additionally made the endpoint return a hash of every banner’s content material, so we will uniquely determine every banner. This shall be helpful once we need to make the banners dismissable and keep in mind if the present banner has been dismissed or not.

This is an instance of the straightforward JSON response it may return:

➜  ~ curl
  "theme": "celebratory",
  "textual content": "We received greatest place to work 2022!!!11",
  "hyperlink": "",
  "hash": "0f8a02f8e424c95d9768ecfb8cf5ac5772c6d0ef5706fde819f540375d39d93b"
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or in darker occasions:

➜  ~ curl
  "theme": "emergency",
  "textual content": "One thing dangerous has occurred, however all our workers are secure. We're posting updates on our Twitter web page.",
  "hyperlink": "",
  "hash": "d98d74b647b5eb02ce1cde89001532df2820758b11c70fa78b53d0e72080aa3e"
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However how one can flip this JSON into HTML, inserted throughout a spread of various websites, all on totally different tech stacks and linked to their very own CMSs, and even inserted into static content material with no CMS in any respect? Enter, ✨the sting✨…

What’s ‘the sting’? (‘the Edge’? ‘The Edge?’ 🤷‍♂️)

Let’s ask Google and Cloudflare:

Edge computing is a networking philosophy centered on bringing computing as near the supply of knowledge as potential in an effort to cut back latency and bandwidth use. In less complicated phrases, edge computing means operating fewer processes within the cloud and shifting these processes to native locations, reminiscent of on a consumer’s laptop, an IoT machine, or an edge server [like a CDN]. Bringing computation to the community’s edge minimizes the quantity of long-distance communication that has to occur between a shopper and server.

For the context of this text, the Edge shall be our CDN, and we will program it utilizing instruments like Cloudflare Staff, Netlify Edge Features, [email protected] (AWS), Akamai EdgeWorkers, or Fastly [email protected], and so forth.

These instruments permit us to change the community response because it passes by way of the sting/CDN layer, for instance modifying the headers or the physique of a response.

I exploit Cloudflare Staff to supply a ‘no JS‘ and ‘no CSS‘ model of my private web site, as a means for me to test how the location seems to be with no CSS (this offers you clues as as to if somebody is utilizing semantic HTML components or not) and the way the location works with JavaScript blocked or disabled (or once I’ve written such horrible JavaScript that the entire thing falls over). These staff take away script or style-related HTML components and in addition add an x-robots-tag HTTP header to forestall engines like google from indexing these pages.

Including a world messages banner through the sting

If I can take away CSS and <script> components from my website with a Cloudflare employee, then it needs to be simple to additionally use them to add in some content material.

Think about considered one of our firm web sites is, a reserved area identify for use in documentation and instance content material so secure for us to mess around with at present.

This is usually:

And here is when run by way of our Cloudflare Employee. If we owned we may stick the employee in entrance of it, so anybody requesting would see the banner. For now, although, we will see the banners by visiting

Screenshot of but now showing a black and white 'We are saddened by X and wish Y' banner at the top of the page

How is that is working?

I do not personal, I do not know the way it will get up to date or what sort of expertise it runs on, however I’ve added a banner to the highest of it. Should you reload the web page you may see the opposite banners seem randomly, as the instance API returns totally different content material every time.

Screenshot of but now showing a colourful 'We won best place to work 2022' banner at the top of the page

Screenshot of but now showing a red 'Something bad has happened, but all our staff are safe. We are posting updates on our Twitter page' banner at the top of the page

We may do the very same factor for every other website our firm owned. Right here I’ve put the employee in entrance of a kind of ‘greatest mom––––ing web site’ web sites…

Screenshot of mother f u c k ing but now showing a colourful 'We won best place to work 2022' banner at the top of the page

…and in entrance of Wikipedia:

Screenshot of Wikipedia but now showing a red 'Something bad has happened, but all our staff are safe. We are posting updates on our Twitter page' banner at the top of the page

The purpose is that if all of your websites had been behind Cloudflare, AWS Cloudfront with [email protected], Akamai EdgeWorkers, Fastly [email protected], all hosted on Netlify, or on any of the opposite companies providing edge staff then we may run the identical employee on all of them, and one central supply of banner content material may replace all of those totally different websites with out ever needing to even open their CMS or their codebase. That is the ability of edge capabilities!

Present me the code!

A lot of the edge operate suppliers present a straightforward solution to rewrite the content material of the web page. That is nice for doing issues like A/B testing or cookie banners with out heavy JavaScript dependence. In Cloudflare’s case we use a HTMLRewriter class.

This is a simplified model the place we use a employee to retrieve some knowledge and add some HTML, JavaScript and CSS to the web page, in addition to modify the Cache-Management header of the web page:

addEventListener("", (occasion) => {

const getData = async () => {
  const response = await fetch(
  const json = await response.json();
  return json;

class HeadHandler {
  constructor(knowledge) {
    this.knowledge = knowledge;
    // Please excuse using a third-party origin CDN,
    // I would not do that in prod…
    this.types = `<hyperlink rel="stylesheet" href="https://cdn.jsdelivr.internet/npm/[email protected]/herald.css" integrity="sha256-zQLpc/AA/o1D8NgVLASianBlbMPs9i4carXMzf/L4mY=" crossorigin="nameless">`;
    this.scripts = `<script src="https://cdn.jsdelivr.internet/npm/[email protected]/herald.js" integrity="sha256-AcoJNZAkXVxpi/5ZW/CXeUadY0z5rEH7h/3OAs5HnTg=" crossorigin="nameless"></script><script>let key = "${knowledge.hash}"; let savedKey = localStorage.getItem("banner--cta-url"); if(savedKey === key) { doc.documentElement.classList.add("banner--hide"); }</script>`;

  ingredient(ingredient) {
      .append(this.types, { html: true })
      .append(this.scripts, { html: true });

class BodyHandler {
  constructor(knowledge) {
    this.knowledge = knowledge;

    this.bannerTemplate = `<announcement-banner data-banner-key="${
    }" data-theme="${knowledge.theme}"> ${
      knowledge.hyperlink ? `<a href="${knowledge.hyperlink}">` : ""
    } ${knowledge.textual content} ${
      knowledge.hyperlink ? `</a>` : ""
    } <button sort="button" data-banner-close>Shut</button></announcement-banner>`;

  ingredient(ingredient) {
      .prepend(this.bannerTemplate, { html: true });

async operate handleRequest() {
  const knowledge = await getData();

  // In real-world utilization the under line would not be crucial as
  // we might work with the present request.
  const response = await fetch("";

  const transformedResponse = new HTMLRewriter()
    .on("", new HeadHandler(knowledge))
    .on("", new BodyHandler(knowledge))

  // Do not cache the web page in order that we will replace the banner simply.
  transformedResponse.headers.set("", ", must-revalidate";
  return transformedRes;
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A little bit bit concerning the banner itself

The main target of this demonstration was the power to inject the banner into any web page, reasonably than the precise banner itself, however in the event you’ve performed with the demo you may discover just a few issues.

The banner seems instantly together with the remainder of the web page content material and causes no format shift. It’s because the HTML for the banner arrives alongside the HTML of the remainder of the web page. If we used a React/Preact/Vue/Alpine part to load the JSON from the instance endpoint after which render a banner we might see a format shift because the banner content material would seem after the remainder of the web page had been laid out.

The banner is dismissible, and in the event you reload the web page just a few occasions you will not see that banner once more till you dismiss a distinct banner. It’s because every banner is given a novel key, and Zach Leatherman’s ‘herald of the canine’ <announcement-banner> net part remembers the final banner to have been dismissed and will not present it once more. Some JavaScript within the <head> of the web page makes certain there is no such thing as a flicker of the banner earlier than it’s hidden (JavaScript within the <head> runs previous to the browser rendering something).

The banner is positioned on the prime of the web page. I believe that is the most secure choice. It is injected proper after the opening <physique> tag. It might be tempting to additionally attempt to add it at the beginning of <most important> or proper after <header> to have it seem under a website’s header in a hero-ish spot, however suppose how that might work with the not-very-semantic markup generated by your jobs board website, or with a JavaScript-dependent SPA whose whole HTML content material is principally <physique><div id="root"></div><noscript>Lol, sorry!</noscript></physique>.

The banner has totally different themes. I believe that is important for a versatile system. You may need a enjoyable theme for excellent news, a purple emergency theme for when one thing dangerous goes down, and a tragic/sombre theme for moments of company reflection and sympathy. We handle the theme through a knowledge attribute on the banner part and a few CSS that we inject into the web page. I may have labored more durable on this side and used a extra thorough means of stopping web page types from bleeding into the banner (all: unset or scoped CSS in a Internet Part), however that wasn’t the main focus of this weblog put up.

Should you wanted to make slight tweaks for various websites then that might be managed in just a few methods. Content material tweaks could be dealt with within the employee, and styling tweaks could be managed by adjusting the specificity of the banner’s CSS (to permit some site-specific websites to use), or by creating modified themes, for instance celebratory--dense for a extra compact celebratory banner to make use of on a webapp reasonably than a advertising and marketing website.

In conclusion

I believe edge staff are GREAT. We are able to launch closely cached and static web sites, however add a layer of dynamism on prime, all managed by our CDN supplier. We are able to form community requests as they cross by way of the CDN, and use this so as to add content material to any HTML response, no matter the place that website is hosted or how it’s maintained. Even a useless website on a server nobody is aware of how one can entry may nonetheless have content material added to it, so long as its area identify might be pointed on the CDN service.

For a state of affairs the place a number of totally different websites have to all present content material from a single supply, that is essentially the most performant and best to implement resolution that I believe I can consider, and positively one thing I would be completely happy to make use of in observe.


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