✨scroll progress on body

browser ⟩ event ⟩ type ⟩ scroll ⟩ example ⟩ scroll progress on body

update the progress bar's width when body.onscroll. (body's height is fixed)

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(200);

// ⭐️ event handlers
// -------------------------------------------------------

// body.onscroll (⭐️ windown/html.onscroll also works❗)
body.addEventListener("scroll", () => {
    const maxScroll = body.scrollBox.height - body.paddingBox.height; // Element+boxes
    const currentScroll = body.scrollBox.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}`;
}, true);            // ⭐️ capturing: true (important❗)
// -> see: https://ayase.moe/2018/11/20/scroll-event/

📁 CSS

html, body {
    height: 300px;
    overflow: scroll;    /*  ⭐️ 必須 html, body 兩者都設定才有效，不知為何？  */
}
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