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import type { FunctionalComponent } from 'preact';
import { h, Fragment } from 'preact';
import { useState, useEffect, useRef } from 'preact/hooks';
const TableOfContents: FunctionalComponent<{ headers: any[] }> = ({ headers = [] }) => {
const itemOffsets = useRef([]);
const [activeId, setActiveId] = useState<string>(undefined);
useEffect(() => {
const getItemOffsets = () => {
const titles = document.querySelectorAll('article :is(h1, h2, h3, h4)');
itemOffsets.current = Array.from(titles).map((title) => ({
id: title.id,
topOffset: title.getBoundingClientRect().top + window.scrollY,
}));
};
getItemOffsets();
window.addEventListener('resize', getItemOffsets);
return () => {
window.removeEventListener('resize', getItemOffsets);
};
}, []);
return (
<>
<h2 class="heading">On this page</h2>
<ul>
<li class={`header-link depth-2 ${activeId === 'overview' ? 'active' : ''}`.trim()}>
<a href="#overview">Overview</a>
</li>
{headers
.filter(({ depth }) => depth > 1 && depth < 4)
.map((header) => (
<li
class={`header-link depth-${header.depth} ${
activeId === header.slug ? 'active' : ''
}`.trim()}
>
<a href={`#${header.slug}`}>{header.text}</a>
</li>
))}
</ul>
</>
);
};
export default TableOfContents;
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