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Join a Group

In order to start participating in group conversations, you will have to join a group. You can do so using the joinGroup() method. 
var GUID = "GUID";
var password = "";
var groupType = CometChat.GROUP_TYPE.PUBLIC;

CometChat.joinGroup(GUID, groupType, password).then(
group => {
  console.log("Group joined successfully:", group);
}, error => {
  console.log("Group joining failed with exception:", error);
}
);
The joinGroup() method takes the below parameters
ParameterDescription
GUIDThe GUID of the group you would like to join.
groupTypeType of the group. CometChat provides 3 types of groups viz. 1. CometChat.GROUP_TYPE.PUBLIC 2. CometChat.GROUP_TYPE.PASSWORD 3. CometChats.GROUP_TYPE.PRIVATE
passwordPassword is mandatory in case of a password protected group.
Once you have joined a group successfully, you can send and receive messages in that group. CometChat keeps a track of the groups joined and you do not need to join the group every time you want to communicate in the group. You can identify if a group is joined using the hasJoined parameter in the Group object.

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Real-time Group Member Joined Events

In other words, as a member of a group, how do I know if someone joins the group when my app is running? If a user joins any group, the members of the group receive a real-time event in the onGroupMemberJoined() method of the GroupListener class. 
CometChat.addGroupListener(
  "UNIQUE_LISTNER_ID",
  new CometChat.GroupListener({
      onGroupMemberJoined: (message, joinedUser, joinedGroup) => {
          console.log("User joined", { message, joinedUser, joinedGroup });
      }
  })
);

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Missed Group Member Joined Events

In other words, as a member of a group, how do I know if someone joins the group when my app is not running? When you retrieve the list of previous messages if a member has joined 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 joined event, in the Action object received, the following fields can help you get the relevant information-
  1. action - joined
  2. actionBy - User object containing the details of the user who joined the group
  3. actionFor- Group object containing the details of the group the user has joined