Sticky without "position: sticky" (top 0)

inspired by https://codepen.io/rikschennink/pen/yZYbwQ

by Roberto Apasajja

HTML

<div id="zirafah">I'm a header, beep boop.</div>

<main>
<p>Contrary to popular belief, Lorem Ipsum is not simply random text. It has roots in a piece of classical Latin literature from 45 BC, making it over 2000 years old. Richard McClintock, a Latin professor at Hampden-Sydney College in Virginia, looked up one of the more obscure Latin words, consectetur, from a Lorem Ipsum passage, and going through the cites of the word in classical literature, discovered the undoubtable source. Lorem Ipsum comes from sections 1.10.32 and 1.10.33 of "de Finibus Bonorum et Malorum" (The Extremes of Good and Evil) by Cicero, written in 45 BC. This book is a treatise on the theory of ethics, very popular during the Renaissance. The first line of Lorem Ipsum, "Lorem ipsum dolor sit amet..", comes from a line in section 1.10.32.</p>

	<p>The standard chunk of Lorem Ipsum used since the 1500s is reproduced below for those interested. Sections 1.10.32 and 1.10.33 from "de Finibus Bonorum et Malorum" by Cicero are also reproduced in their exact original form, accompanied by English versions from the 1914 translation by H. Rackham.</p>
	
	<p>Contrary to popular belief, Lorem Ipsum is not simply random text. It has roots in a piece of classical Latin literature from 45 BC, making it over 2000 years old. Richard McClintock, a Latin professor at Hampden-Sydney College in Virginia, looked up one of the more obscure Latin words, consectetur, from a Lorem Ipsum passage, and going through the cites of the word in classical literature, discovered the undoubtable source. Lorem Ipsum comes from sections 1.10.32 and 1.10.33 of "de Finibus Bonorum et Malorum" (The Extremes of Good and Evil) by Cicero, written in 45 BC. This book is a treatise on the theory of ethics, very popular during the Renaissance. The first line of Lorem Ipsum, "Lorem ipsum dolor sit amet..", comes from a line in section 1.10.32.</p>

	<p>The standard chunk of Lorem Ipsum used since the 1500s is reproduced below for those...

CSS

body {
  margin: 0;
  height: 2000px;
}

#zirafah {
  width: 100%;
  min-height: 3em;
  background-color: magenta;
}

html:not([data-scroll='0']) body {
  padding-top: 3em;
}
html:not([data-scroll='0']) #zirafah {
  position: fixed;
  top: 0;
  background-color: grey;
}

JavaScript

// The debounce function receives our function as a parameter
const debounce = (fn) => {

  // This holds the requestAnimationFrame reference, so we can cancel it if we wish
  let frame;

  // The debounce function returns a new function that can receive a variable number of arguments
  return (...params) => {
    
    // If the frame variable has been defined, clear it now, and queue for next frame
    if (frame) { 
      cancelAnimationFrame(frame);
    }

    // Queue our function call for the next frame
    frame = requestAnimationFrame(() => {
      
      // Call our function and pass any params we received
      fn(...params);
    });

  } 
};


// Reads out the scroll position and stores it in the data attribute
// so we can use it in our stylesheets
const storeScroll = () => {
  document.documentElement.dataset.scroll = window.scrollY;
}

// Listen for new scroll events, here we debounce our `storeScroll` function
document.addEventListener('scroll', debounce(storeScroll), { passive: true });

// Update scroll position for first time
storeScroll();