Add scroll progress bar

snippets/scroll-progress-bar.md

@@ -0,0 +1,40 @@
+---
+title: Scroll progress bar
+tags: animation,visual,intermediate
+---
+
+Creates a progress bar indicating the scroll percentage of the page.
+
+- Use `position: fixed` and a large `z-index` value to place the element at the top of the page and above any content.
+- Use `EventTarget.addEventListener()` along with `Element.scrollTop` to determine the scroll percentage of the document and apply it to the `width` of the element.
+
+```html
+<div id="scroll-progress"></div>
+```
+
+```css
+body {
+  min-height: 200vh;
+}
+
+#scroll-progress {
+  position: fixed;
+  top: 0;
+  width: 0%;
+  height: 4px;
+  background: #7983ff;
+  z-index: 10000;
+}
+```
+
+```js
+const scrollProgress = document.getElementById('scroll-progress');
+const height =
+  document.documentElement.scrollHeight - document.documentElement.clientHeight;
+
+window.addEventListener('scroll', () => {
+  const scrollTop =
+    document.body.scrollTop || document.documentElement.scrollTop;
+  scrollProgress.style.width = `${(scrollTop / height) * 100}%`;
+});
+```