A few days ago, I was working on JSOM (JavaScript object model) on SharePoint Online. As per the business requirement, I had to check if he/she is a member of a particular SP Group or not. In that scenario, I used the following code.

Steps to use the code

To use the code, this function can be added to the targeted code file or to use in a SharePoint custom list forms or in a page. Adding to the Script Editor web part or Content Editor web part will be a good choice.

The following function named "IsGroupMember" is the function which returns a boolean value with True/False. And this function gets three parameters - the name of the Group, the user from whom we want to check, and the ClientContext. Also, it is important to mention that with groupName variable, a string value as the group visual name needs to be sent and with cUser variable, SPUser's user name needs to be sent.

Code Snippet
  1. function IsGroupMember(groupName, cUser, clientContext) {
  2. var deferred = $.Deferred();
  3. var currentWeb = clientContext.get_web();
  5. var allGroups = currentWeb.get_siteGroups();
  6. clientContext.load(allGroups);
  8. var group = allGroups.getByName(groupName);
  9. clientContext.load(group);
  11. var groupUsers = group.get_users();
  12. clientContext.load(groupUsers);
  14. clientContext.executeQueryAsync(
  15. function onQuerySucceeded(sender, args) {
  16. var isUserInGroup = false;
  17. var groupUserEnumerator = groupUsers.getEnumerator();
  18. while (groupUserEnumerator.moveNext()) {
  19. var groupUser = groupUserEnumerator.get_current();
  20. if (groupUser.get_id() == cUser.get_id()) {
  21. isUserInGroup = true;
  22. break;
  23. }
  24. }
  25. deferred.resolve(isUserInGroup);
  26. },
  27. function onQueryFailed(sender, args) {
  28. console.log('Request failed. ' + args.get_message() + '\n' + args.get_stackTrace());
  29. deferred.resolve(false);
  30. //if the funtion got ay error, it will return false.
  31. }
  32. );
  33. return deferred.promise();
  34. }

Notes
In this code snippet, deferred - promise is used to increase the usability. This can be ignored if the developer wants to simply return the value or can use onComplete function.