41 lines
1.3 KiB
JavaScript
41 lines
1.3 KiB
JavaScript
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/* Back-to-top: erscheint nach ~1,5 Viewporthöhen Scrolltiefe.
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Sanftes Scrollen kommt aus dem CSS (scroll-behavior + reduced-motion-Kill-Switch);
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JS übernimmt Sichtbarkeit und Fokus-Management. Ohne JS bleibt der Button hidden. */
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(function () {
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'use strict';
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var button = document.querySelector('.back-to-top');
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var main = document.getElementById('main');
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if (!button || !main) {
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return;
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}
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button.hidden = false;
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var ticking = false;
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function update() {
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button.classList.toggle('is-visible', window.scrollY > window.innerHeight * 1.5);
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ticking = false;
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}
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window.addEventListener('scroll', function () {
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if (!ticking) {
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ticking = true;
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window.requestAnimationFrame(update);
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}
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}, { passive: true });
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update();
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// Deep-Link-Einstiege (#anker): Sprung passiert teils vor dem Listener-Setup.
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window.addEventListener('load', update);
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button.addEventListener('click', function (event) {
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event.preventDefault();
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var reduced = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
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window.scrollTo({ top: 0, behavior: reduced ? 'auto' : 'smooth' });
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// Fokus an den Seitenanfang mitnehmen (Tastatur/Screenreader).
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main.focus({ preventScroll: true });
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});
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})();
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