ECMA script to check if user is a member of sharepoint group

Hi All,

I need to check if the current user belongs to s particular SP group using ECMA script. I have written the following code

function CheckIfCurrentUserIsCoordinator() {

    var clientContext = new SP.ClientContext.get_current();
    this.collGroup = clientContext.get_web().get_siteGroups();
    clientContext.load(collGroup);
    clientContext.load(collGroup, 'Include(Users)');

    this.currentUser = clientContext.get_web().get_currentUser();
    clientContext.load(currentUser);   

    clientContext.executeQueryAsync(Function.createDelegate(this, this.onQuerySucceeded), Function.createDelegate(this, this.onQueryFailed));
}

function onQuerySucceeded(sender, args) {

    var UserExistInGroup = false;  
    var groupEnumerator = collGroup.getEnumerator();
    while (groupEnumerator.moveNext()) {
    var oGroup = groupEnumerator.get_current();
    if(oGroup.get_title()=='Group A')
    {
    var collUser = oGroup.get_users();
    var userEnumerator = collUser.getEnumerator();
    while (userEnumerator.moveNext()) {
           var oUser = userEnumerator.get_current();
           if (oUser.get_loginName() == currentUser.get_loginName()) {
                UserExistInGroup = true;           
                break;
            }
        }
    }

    if(UserExistInGroup)
    {
    break;
    } 
   }   
   if(UserExistInGroup)
   {      
	//code
   }   
    

}

function onQueryFailed(sender, args) {

    alert('Request failed. ' + args.get_message() + '\n' + args.get_stackTrace());
}

The code works fine if i log-in as a site collection owner. If i log-in as any other user having contribute access on site I get following error message

"Access Denied. You do not have permission to perform this action or access this resource."

What permission do i need to give users so that they can loop through all site groups and users?

Thanks,

Ameya