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Leave a Group

In order to stop receiving updates and messages for any particular joined group, you will have to leave the group using the leaveGroup() method. 
var GUID = "GUID";

CometChat.leaveGroup(GUID).then(
hasLeft => {
  console.log("Group left successfully:", hasLeft);
}, error => {
  console.log("Group leaving failed with exception:", error);
}
);
ParameterDescription
GUIDThe UID of the group you would like to leave
Once a group is left, the user will no longer receive any updates or messages pertaining to the group.

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Real-time Group Member Left Events

In other words, as a member of a group, how do I know if someone has left it? If a user leaves any group, The members of the group receive a real-time event in the onGroupMemberLeft() method of the GroupListener class. 
CometChat.addGroupListener(
  "UNIQUE_LISTENER_ID",
  new CometChat.GroupListener({
      onGroupMemberLeft: (message, leavingUser, group) => {
          console.log("User left", { message, leavingUser, group });
      }
  })
);

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Missed Group Member Left Events

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