SharePoint Online Environment:
var isHelpDeskUser = False;
$(function() {
ValidationForHelpDesk();
});
function ValidationForHelpDesk(){
var url = _spPageContextInfo.webAbsoluteUrl +'/_api/web/currentuser/groups'
$.getJSON(url, function (data) {
$.each(data.value, function (key, value) {
if (value.Title == 'SAGroup') { //SharePoint HelpDesk Group name is SAGroup
isHelpDeskUser = true;
}
});
})
}
If Current User is part of "SAGroup" then variable isHelpDeskUser will set to true;
        
    
   
var isHelpDeskUser = False;
$(function() {
ValidationForHelpDesk();
});
function ValidationForHelpDesk(){
var url = _spPageContextInfo.webAbsoluteUrl +'/_api/web/currentuser/groups'
$.getJSON(url, function (data) {
$.each(data.value, function (key, value) {
if (value.Title == 'SAGroup') { //SharePoint HelpDesk Group name is SAGroup
isHelpDeskUser = true;
}
});
})
}
If Current User is part of "SAGroup" then variable isHelpDeskUser will set to true;
SharePoint On Premise environment:
 function ValidationForHelpDesk(){
 CurrentUserMemberOfGroup("
   if(isCurrentUserInGroup)  
   {       
      console.log('user is member of the group'); 
      isHelpDeskUser = true;
   }  
   else  
   {        
   console.log('user is not member of the group'); 
   isHelpDeskUser = false; 
   }
 });
}//Function Close
function CurrentUserMemberOfGroup(
        var ctx = new SP.ClientContext.get_current()
        var currentUser = ctx.get_web().get_currentUser(
        ctx.load(currentUser);   
        var Groups = ctx.get_web().get_siteGroups()
        ctx.load(Groups);   
        var group = Groups.getByName(groupName);  
        ctx.load(group);          
        var groupUsers = group.get_users();  
        ctx.load(groupUsers);
        ctx.executeQueryAsync(  
                function(sender, args) {  
                   var userInGroup = UserInGroup(currentUser,group)
                   OnComplete(userInGroup);  
                },  
                function OnFailure(sender, args) {  
                   OnComplete(false);  
                }  
        );            
        function UserInGroup(user,group)  
        {  
            var groupUsers = group.get_users();  
            var userInGroup = false;  
            var groupUserEnumerator = groupUsers.getEnumerator();  
            while (groupUserEnumerator.moveNext(
                var groupUser = groupUserEnumerator.get_
                if (groupUser.get_id() == user.get_id()) {  
                    userInGroup = true;  
                    break;  
                }  
            }  
            return userInGroup;  
        }  
}
