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Add Members to Group

You can add members to the group using the addMembersToGroup() method. This method takes the below parameters:
  1. GUID - GUID of the group the members are to be added to.
  2. members - This is a list of GroupMember objects. In order to add members, you need to create an object of the GroupMember class. The UID and the scope of the GroupMember are mandatory.
  3. bannedMembers - This is the list of UID's that need to be banned from the Group. This can be set to null if there are no members to be banned.
let GUID = "GUID";
let UID = "UID";
let membersList = [
  new CometChat.GroupMember(UID, CometChat.GROUP_MEMBER_SCOPE.PARTICIPANT),
];

CometChat.addMembersToGroup(GUID, membersList, []).then(
  (response) => {
    console.log("response", response);
  },
  (error) => {
    console.log("Something went wrong", error);
  }
);
It will return a Array which will contain the UID of the users and the value will either be success or an error message describing why the operation to add the user to the group.

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Real-Time Group Member Added Events

In other words, as a member of a group, how do I know when someone is added to the group when my app is running?
When a group member is added by another member, this event is triggered. When a user joins a group on their own, the joined event is triggered.
To receive real-time events whenever a new member is added to a group, you need to implement the onMemberAddedToGroup() methods of the GroupListener class. onMemberAddedToGroup() - This method is triggered when any user is added to the group so that the logged in user is informed of the other members added to the group. 
var listenerID = "UNIQUE_LISTENER_ID";

CometChat.addGroupListener(
  listenerID,
  new CometChat.GroupListener({
    onMemberAddedToGroup: (message, userAdded, userAddedBy, userAddedIn) => {
      console.log("User joined", {
        message,
        userAdded,
        userAddedBy,
        userAddedIn,
      });
    },
  })
);

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Member Added to Group event in Message History

In other words, as a member of a group, how do I know when someone is added to the group when my app is not running? When you retrieve the list of previous messages if a member has been added to any group that the logged-in user is a member of, the list of messages will contain an Action message. An Action message is a sub-class of BaseMessage class. For the group member added event, in the Action object received, the following fields can help you get the relevant information-
  1. action - added
  2. actionOn - User object containing the details of the user who was added to the group
  3. actionBy - User object containing the details of the user who added the member to the group
  4. actionFor - Group object containing the details of the group to which the member was added