browser ⟩ event ⟩ type ⟩ scroll ⟩ example ⟩ scroll progress
update the progress bar's width onscroll. (body's height is automatic)
const { log } = console
// ⭐️ import
import { $ } from './js/ext/Node_ext.js'; // Node+ext
import { viewport } from './js/ext/Element+boxes.js'; // Element+boxes
// --------------------------------------------------------------------
// elements
const html = document.documentElement; // <HTML>
const body = document.body; // <BODY>
const bar = $("#progress"); // Node + ext
const info = $("#info");
const content = $('#content');
content.textContent = "supercali fragilisti cexpiali docious ".repeat(500);
// ⭐️ event handlers
// -------------------------------------------------------
// window.onscroll
window.addEventListener("scroll", () => {
// same as: `html.scrollHeight - innerHeight`
const maxScroll = html.scrollBox.height - viewport.height; // Element+boxes
const currentScroll = viewport.y; // Element+boxes
const percent = (currentScroll / maxScroll) * 100;
// update UI
bar.style.width = `${percent}%`;
bar.textContent = `${percent.toFixed(0)}%`;
info.textContent = `scroll amout: ${currentScroll} / max: ${maxScroll}`;
});