44 lines
1.3 KiB
JavaScript
44 lines
1.3 KiB
JavaScript
export const createPlaceholder = () => {
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const placeholder = document.createElement('div');
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placeholder.classList.add('sticky-placeholder');
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return placeholder;
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};
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export const isSticky = (el, scrollY, stickyTop, insertPlaceholder) => {
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const top = Math.floor(el.offsetTop - scrollY);
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if (top <= stickyTop && !el.classList.contains('is-stuck')) {
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const placeholder = insertPlaceholder ? createPlaceholder() : null;
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const heightBefore = el.offsetHeight;
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el.classList.add('is-stuck');
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if (insertPlaceholder) {
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el.parentNode.insertBefore(placeholder, el.nextElementSibling);
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placeholder.style.height = `${heightBefore - el.offsetHeight}px`;
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}
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} else if (top > stickyTop && el.classList.contains('is-stuck')) {
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el.classList.remove('is-stuck');
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if (insertPlaceholder && el.nextElementSibling && el.nextElementSibling.classList.contains('sticky-placeholder')) {
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el.nextElementSibling.remove();
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}
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}
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};
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export default (el, insertPlaceholder = true) => {
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if (!el) return;
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const computedStyle = window.getComputedStyle(el);
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if (!/sticky/.test(computedStyle.position)) return;
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const stickyTop = parseInt(computedStyle.top, 10);
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document.addEventListener('scroll', () => isSticky(el, window.scrollY, stickyTop, insertPlaceholder), {
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passive: true,
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});
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};
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