useIntersectionObserver

components/Table/Table.tsx

@@ -1,4 +1,7 @@
 import type { CSSProperties } from 'react';
+import { useEffect } from 'react';
+
+import { useIntersectionObserver } from '../../hooks/useIntersectionObserver';
 
 import styles from './table.module.scss';
 import { useFloatingTableHeader } from './useFloatingTableHeader';
@@ -28,16 +31,24 @@ const TableHeaderRow = ({
   );
 };
 
+const intersectionObserverOptions = {};
+
 export const Table = <T extends { readonly id: string }>({ data, columns }: TableProps<T>) => {
   const { tableRef, floatingHeaderRef } = useFloatingTableHeader<HTMLDivElement>();
 
+  const { setRef, entry } = useIntersectionObserver<HTMLTableSectionElement>(
+    intersectionObserverOptions,
+  );
+
+  console.log({ entry });
+
   return (
     <div className={styles.tableWrapper}>
       <div ref={floatingHeaderRef} aria-hidden={true}>
         <TableHeaderRow columns={columns} as="span" />
       </div>
       <table ref={tableRef} className={styles.table}>
-        <thead>
+        <thead ref={setRef}>
           <tr>
             <TableHeaderRow columns={columns} as="th" />
           </tr>

hooks/useIntersectionObserver.tsx

@@ -0,0 +1,100 @@
+import { useCallback, useEffect, useRef, useState } from 'react';
+
+import { useWillUnmount } from './useWillUnmount';
+
+type UseIntersectionObserverArgs = Pick<IntersectionObserverInit, 'rootMargin' | 'threshold'>;
+type ObserverCallback = (entry: IntersectionObserverEntry) => void;
+type Observer = {
+  readonly key: string;
+  readonly intersectionObserver: IntersectionObserver;
+  // eslint-disable-next-line
+  readonly elementToCallback: Map<Element, ObserverCallback>;
+};
+
+export const useIntersectionObserver = <T extends Element = HTMLElement>(
+  options: UseIntersectionObserverArgs,
+) => {
+  const unobserve = useRef<() => void>();
+
+  const [entry, setEntry] = useState<IntersectionObserverEntry | null>(null);
+
+  const setRef = useCallback(
+    (el: T) => {
+      console.log({ el });
+
+      if (unobserve.current) {
+        unobserve.current();
+        unobserve.current = undefined;
+      }
+
+      if (el && el.tagName) {
+        unobserve.current = observe(el, setEntry, options);
+      }
+    },
+    [options],
+  );
+
+  useWillUnmount(() => {
+    if (unobserve.current) {
+      unobserve.current();
+      unobserve.current = undefined;
+    }
+  });
+
+  if (typeof window === 'undefined' || typeof IntersectionObserver === 'undefined') {
+    return { setRef: () => {}, entry: null } as const;
+  }
+
+  return { setRef, entry } as const;
+};
+
+const observe = (() => {
+  const observers = new Map<string, Observer>();
+
+  const createObserver = (options: UseIntersectionObserverArgs) => {
+    const key = JSON.stringify(options);
+    if (observers.has(key)) {
+      return observers.get(key)!;
+    }
+
+    const elementToCallback = new Map<Element, ObserverCallback>();
+    const intersectionObserver = new IntersectionObserver((entries) => {
+      entries.forEach((entry) => {
+        const callback = elementToCallback.get(entry.target);
+        if (callback) {
+          callback(entry);
+        }
+      });
+    }, options);
+
+    const observer: Observer = {
+      key,
+      elementToCallback,
+      intersectionObserver,
+    };
+    observers.set(key, observer);
+
+    return observer;
+  };
+
+  return <T extends Element>(
+    el: T,
+    callback: ObserverCallback,
+    options: UseIntersectionObserverArgs,
+  ) => {
+    const { key, elementToCallback, intersectionObserver } = createObserver(options);
+    elementToCallback.set(el, callback);
+    intersectionObserver.observe(el);
+
+    const unobserve = () => {
+      intersectionObserver.unobserve(el);
+      elementToCallback.delete(el);
+
+      if (elementToCallback.size === 0) {
+        intersectionObserver.disconnect();
+        observers.delete(key);
+      }
+    };
+    return unobserve;
+  };
+})();

hooks/useWillUnmount.tsx

@@ -0,0 +1,7 @@
+import type { EffectCallback } from 'react';
+import { useEffect } from 'react';
+
+/* eslint-disable react-hooks/exhaustive-deps */
+export const useWillUnmount = (cb: ReturnType<EffectCallback>) => {
+  useEffect(() => cb, []);
+};