fix: scrolling

src/client/chat--messages.jsx

@@ -1,6 +1,11 @@
 import './chat--messages.scss';
 
-import React, {useLayoutEffect, useRef} from 'react';
+import React, {
+  useEffect,
+  useLayoutEffect,
+  useRef,
+  useState,
+} from 'react';
 import {useSelector} from 'react-redux';
 
 import {channelMessagesSelector} from '~/common/state/chat';
@@ -16,23 +21,35 @@ export default function ChatMessages() {
   const channel = useChannel();
   const $messages = useRef(null);
   const {current} = $messages;
-  const isAtTheBottom = !current
-    ? true
-    : 0 === current.scrollTop || (
-      current.scrollHeight
-      === current.scrollTop
-        + ['margin-top', 'margin-bottom'].reduce((r, property) => (
-          r + parseInt(window.getComputedStyle(current).getPropertyValue(property), 10)
-        ), current.offsetHeight)
-    );
-  const heightWatch = current && current.scrollHeight;
+  const [, setIsAtBottom] = useState(true);
+  const [outerHeight, setOuterHeight] = useState(0);
+  const [scrollTop, setScrollTop] = useState(0);
+  const [scrollHeight, setScrollHeight] = useState(Infinity);
   const messages = useSelector((state) => channelMessagesSelector(state, channel));
   const messageCount = messages && messages.length;
+  useEffect(() => {
+    const onResize = () => {
+      setOuterHeight(
+        !current
+          ? 0
+          : ['margin-top', 'margin-bottom'].reduce((r, property) => (
+            r + parseInt(window.getComputedStyle(current).getPropertyValue(property), 10)
+          ), current.offsetHeight),
+      );
+      setScrollHeight(!current ? 0 : current.scrollHeight);
+    };
+    window.addEventListener('resize', onResize);
+    onResize();
+  });
   useLayoutEffect(() => {
-    if (isAtTheBottom) {
-      current?.scrollTo(0, !current ? 0 : current.scrollHeight);
+    const isAtBottom = !current
+      ? true
+      : 0 === scrollTop || scrollTop + outerHeight >= scrollHeight;
+    setIsAtBottom(isAtBottom);
+    if (isAtBottom) {
+      current?.scrollTo(0, scrollHeight);
     }
-  }, [current, heightWatch, messageCount, isAtTheBottom]);
+  }, [current, messageCount, outerHeight, scrollHeight, scrollTop]);
   if (!channel) {
     return null;
   }
@@ -42,6 +59,7 @@ export default function ChatMessages() {
       <div className="chat--messagesSmoosh" />
       <div
         className="chat--messagesList"
+        onScroll={({target: {scrollTop}}) => setScrollTop(Math.round(scrollTop))}
         ref={$messages}
       >
         {messages && messages.map((message) => {