Determine if current user is a member of Group via CSOM(JavaScript) in SharePoint 2010/2013

SP.IsCurrentUserMemberOfGroup.Example.js

//Usage
function IsCurrentUserWithContributePerms() 
{
  IsCurrentUserMemberOfGroup("Members", function (isCurrentUserInGroup) {
    if(isCurrentUserInGroup)
    {
        // The current user is in the [Members] group
    }
  });

}
ExecuteOrDelayUntilScriptLoaded(IsCurrentUserWithContributePerms, 'SP.js');

SP.IsCurrentUserMemberOfGroup.js

function IsCurrentUserMemberOfGroup(groupName, OnComplete) {
 
        var context = new SP.ClientContext.get_current();
        var currentWeb = context.get_web();
 
        var currentUser = context.get_web().get_currentUser();
        context.load(currentUser);
 
        var allGroups = currentWeb.get_siteGroups();
        context.load(allGroups);
 
        var group = allGroups.getByName(groupName);
        context.load(group);
        
        var groupUsers = group.get_users();
        context.load(groupUsers);
 
        context.executeQueryAsync(
                function(sender, args) {
                   var userInGroup = IsUserInGroup(currentUser,group);         
                   OnComplete(userInGroup);
                },
                function OnFailure(sender, args) {
                   OnComplete(false);
                }
        );
        
        function IsUserInGroup(user,group)
        {
            var groupUsers = group.get_users();
            var userInGroup = false;
            var groupUserEnumerator = groupUsers.getEnumerator();
            while (groupUserEnumerator.moveNext()) {
                var groupUser = groupUserEnumerator.get_current();
                if (groupUser.get_id() == user.get_id()) {
                    userInGroup = true;
                    break;
                }
            }
            return userInGroup;
        }
}

Demonstrates how to determine if current user is a member of specific Group via CSOM(JavaScript) in SharePoint 2010/2013

If anyone is interested. This approach can be used when you want to check if a user is a member of a group using the group name.

[https://gist.github.com/robertosljunior/cc46d4447cf6d6b60c67]

Should come with a proper warning that it just iterates the group. What about AD groups in SharePoint groups? Likely hard to do but worth mentioning that it is not covered.

As @soerennielsen mentioned, this is almost worthless since site administrators / owners can add AD groups to SharePoint Groups.
To be more specific, if the user you need to check membership is member of AD group HR and HR group is added to SharePoint group "Group 1", when you check if the user is actually a member of Group 1, you get false

The only solution for this problem that I can think of is to create a list item with a 'User' column set to the group name. Then query the list with a CAML query that specifies that the current user should be a member of the group in that column. If it comes back in the result, then they're a member.

This is obviously slow but with some caching, maybe it'd be okay. It's the only thing I can think of. Thoughts?

@Johnycardy That's the exact approach we followed. Replying to a 4-year-old thread as the solution you proposed works elegantly.