[Perf] Chat List: Some optimizations

src/components/left/main/ChatList.tsx

@@ -90,11 +90,15 @@ const ChatList: FC<OwnProps & StateProps & DispatchProps> = ({
 
   const prevOrderById = usePrevious(orderById);
 
-  const orderDiffById = orderById && prevOrderById
+  const orderDiffById = useMemo(() => {
-    ? mapValues(orderById, (order, id) => {
+    if (!orderById || !prevOrderById) {
+      return {};
+    }
+
+    return mapValues(orderById, (order, id) => {
       return order - (prevOrderById[id] !== undefined ? prevOrderById[id] : Infinity);
-    })
+    });
-    : {};
+  }, [orderById, prevOrderById]);
 
   const loadMoreOfType = useCallback(() => {
     loadMoreChats({ listType: folderType === 'archived' ? 'archived' : 'active' });

src/lib/teact/teact.ts

@@ -85,8 +85,14 @@ interface ComponentInstance {
   onUpdate?: () => void;
 }
 
-export type VirtualElement = VirtualElementEmpty | VirtualElementText | VirtualElementTag | VirtualElementComponent;
+export type VirtualElement =
-export type VirtualRealElement = VirtualElementTag | VirtualElementComponent;
+  VirtualElementEmpty
+  | VirtualElementText
+  | VirtualElementTag
+  | VirtualElementComponent;
+export type VirtualRealElement =
+  VirtualElementTag
+  | VirtualElementComponent;
 export type VirtualElementChildren = VirtualElement[];
 
 const Fragment = Symbol('Fragment');
@@ -545,7 +551,7 @@ export function useLayoutEffect(effect: () => Function | void, dependencies?: an
   return useLayoutEffectBase(onTickEnd, effect, dependencies);
 }
 
-export function useMemo<T extends any>(resolver: () => T, dependencies: any[]): T {
+export function useMemo<T extends any>(resolver: () => T, dependencies: any[], debugKey?: string): T {
   const { cursor, byCursor } = renderingInstance.hooks.memos;
   let { current } = byCursor[cursor] || {};
 
@@ -553,6 +559,16 @@ export function useMemo<T extends any>(resolver: () => T, dependencies: any[]):
     byCursor[cursor] === undefined
     || dependencies.some((dependency, i) => dependency !== byCursor[cursor].dependencies[i])
   ) {
+    if (DEBUG && debugKey) {
+      // eslint-disable-next-line no-console
+      console.log(
+        `[Teact.useMemo] ${renderingInstance.name} (${debugKey}): Update is caused by:`,
+        byCursor[cursor]
+          ? getUnequalProps(dependencies, byCursor[cursor].dependencies).join(', ')
+          : '[first render]',
+      );
+    }
+
     current = resolver();
   }
 

src/modules/reducers/chats.ts

@@ -100,20 +100,28 @@ export function updateChats(global: GlobalState, updatedById: Record<number, Api
 // @optimization Allows to avoid redundant updates which cause a lot of renders
 export function addChats(global: GlobalState, addedById: Record<number, ApiChat>): GlobalState {
   const { byId } = global.chats;
+  let isAdded = false;
+
   const addedChats = Object.keys(addedById).map(Number).reduce<Record<number, ApiChat>>((acc, id) => {
     if (!byId[id] || (byId[id].isMin && !addedById[id].isMin)) {
       const updatedChat = getUpdatedChat(global, id, addedById[id]);
       if (updatedChat) {
         acc[id] = updatedChat;
+
+        if (!isAdded) {
+          isAdded = true;
+        }
       }
     }
     return acc;
   }, {});
 
-  global = replaceChats(global, {
+  if (isAdded) {
-    ...global.chats.byId,
+    global = replaceChats(global, {
-    ...addedChats,
+      ...global.chats.byId,
-  });
+      ...addedChats,
+    });
+  }
 
   return global;
 }

src/modules/reducers/users.ts

@@ -91,23 +91,30 @@ export function updateUsers(global: GlobalState, updatedById: Record<number, Api
 // @optimization Allows to avoid redundant updates which cause a lot of renders
 export function addUsers(global: GlobalState, addedById: Record<number, ApiUser>): GlobalState {
   const { byId } = global.users;
+  let isAdded = false;
 
   const addedUsers = Object.keys(addedById).map(Number).reduce<Record<number, ApiUser>>((acc, id) => {
     if (!byId[id] || (byId[id].isMin && !addedById[id].isMin)) {
       const updatedUser = getUpdatedUser(global, id, addedById[id]);
       if (updatedUser) {
         acc[id] = updatedUser;
+
+        if (!isAdded) {
+          isAdded = true;
+        }
       }
     }
     return acc;
   }, {});
 
-  global = updateContactList(global, Object.values(addedUsers));
+  if (isAdded) {
+    global = replaceUsers(global, {
+      ...global.users.byId,
+      ...addedUsers,
+    });
 
-  global = replaceUsers(global, {
+    global = updateContactList(global, Object.values(addedUsers));
-    ...global.users.byId,
+  }
-    ...addedUsers,
-  });
 
   return global;
 }