fix: make _hydrateMembers merge objects instead of overriding them

src/channel.ts

@@ -1661,8 +1661,10 @@ export class Channel<StreamChatGenerics extends ExtendableGenerics = DefaultGene
   ) {
     const { state: clientState, user, userID } = this.getClient();
 
-    // add the Users
+    // add the users
     if (state.members) {
+      this._hydrateMembers({ members: state.members });
+
       for (const member of state.members) {
         if (member.user) {
           clientState.updateUserReference(member.user, this.cid);
@@ -1728,10 +1730,6 @@ export class Channel<StreamChatGenerics extends ExtendableGenerics = DefaultGene
       }
     }
 
-    if (state.members) {
-      this._hydrateMembers(state.members);
-    }
-
     return {
       messageSet,
     };
@@ -1747,13 +1745,34 @@ export class Channel<StreamChatGenerics extends ExtendableGenerics = DefaultGene
     }
   }
 
-  _hydrateMembers(members: ChannelMemberResponse<StreamChatGenerics>[]) {
-    this.state.members = members.reduce((acc, member) => {
+  _hydrateMembers({
+    members,
+    overrideCurrentState = true,
+  }: {
+    members: ChannelMemberResponse<StreamChatGenerics>[];
+    /**
+     * If set to `true` then `ChannelState.members` will be overriden with the newly
+     * provided `members`, setting this property to `false` will merge current `ChannelState.members`
+     * object with the newly provided `members`
+     * (new members with the same `userId` will replace the old ones).
+     */
+    overrideCurrentState?: boolean;
+  }) {
+    const newMembersById = members.reduce<ChannelState<StreamChatGenerics>['members']>((membersById, member) => {
       if (member.user) {
-        acc[member.user.id] = member;
+        membersById[member.user.id] = member;
       }
-      return acc;
-    }, {} as ChannelState<StreamChatGenerics>['members']);
+      return membersById;
+    }, {});
+
+    if (overrideCurrentState) {
+      this.state.members = newMembersById;
+    } else if (!overrideCurrentState && members.length) {
+      this.state.members = {
+        ...this.state.members,
+        ...newMembersById,
+      };
+    }
   }
 
   _disconnect() {

src/thread.ts

@@ -78,7 +78,7 @@ export class Thread<SCG extends ExtendableGenerics = DefaultGenerics> {
     const channel = client.channel(threadData.channel.type, threadData.channel.id, {
       name: threadData.channel.name,
     });
-    channel._hydrateMembers(threadData.channel.members ?? []);
+    channel._hydrateMembers({ members: threadData.channel.members ?? [], overrideCurrentState: false });
 
     // For when read object is undefined and due to that unreadMessageCount for
     // the current user isn't being incremented on message.new

test/unit/threads.test.ts

@@ -48,7 +48,9 @@ describe('Threads 2.0', () => {
   beforeEach(() => {
     client = new StreamChat('apiKey');
     client._setUser({ id: TEST_USER_ID });
-    channelResponse = generateChannel({ channel: { id: uuidv4(), name: 'Test channel' } }).channel as ChannelResponse;
+    channelResponse = generateChannel({
+      channel: { id: uuidv4(), name: 'Test channel', members: [] },
+    }).channel as ChannelResponse;
     channel = client.channel(channelResponse.type, channelResponse.id);
     parentMessageResponse = generateMsg() as MessageResponse;
     threadManager = new ThreadManager({ client });
@@ -57,12 +59,16 @@ describe('Threads 2.0', () => {
   describe('Thread', () => {
     it('initializes properly', () => {
       const threadResponse = generateThreadResponse(channelResponse, parentMessageResponse);
+      // mimic pre-cached channel with existing members
+      channel._hydrateMembers({ members: [{ user: { id: TEST_USER_ID } }] });
       const thread = new Thread({ client, threadData: threadResponse });
       const state = thread.state.getLatestValue();
 
+      expect(threadResponse.channel.members).to.have.lengthOf(0);
       expect(threadResponse.read).to.have.lengthOf(0);
       expect(state.read).to.have.keys([TEST_USER_ID]);
 
+      expect(thread.channel.state.members).to.have.keys([TEST_USER_ID]);
       expect(thread.id).to.equal(parentMessageResponse.id);
       expect(thread.channel.data?.name).to.equal(channelResponse.name);
     });