61 lines
1.8 KiB
JavaScript
61 lines
1.8 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 (
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insertPlaceholder &&
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el.nextElementSibling &&
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el.nextElementSibling.classList.contains('sticky-placeholder')
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) {
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el.nextElementSibling.remove();
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}
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}
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};
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/**
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* Create a listener that will toggle a 'is-stuck' class, based on the current scroll position.
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*
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* - If the current environment does not support `position: sticky`, do nothing.
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*
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* @param {HTMLElement} el The `position: sticky` element.
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* @param {Number} stickyTop Used to determine when an element is stuck.
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* @param {Boolean} insertPlaceholder Should a placeholder element be created when element is stuck?
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*/
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export const stickyMonitor = (el, stickyTop, insertPlaceholder = true) => {
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if (!el) return;
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if (
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typeof CSS === 'undefined' ||
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!CSS.supports('(position: -webkit-sticky) or (position: sticky)')
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)
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return;
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document.addEventListener(
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'scroll',
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() => isSticky(el, window.scrollY, stickyTop, insertPlaceholder),
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{
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passive: true,
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},
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);
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};
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