Populate group member based on group selected

[Bindhu1]

I have below 2 variable, based on group selection , group member should get populated [each group has only one member] 
1.approval_group: referring to sys_user_group table
2.approver: referring to sys_user table
tried below script, its not populating member, please help me here
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script include: 

var GetApproverByGroup = Class.create();
GetApproverByGroup.prototype = Object.extendsObject(AbstractAjaxProcessor, {
   getApprover: function() {
       var groupSysId = this.getParameter('sysparm_group');
       var userSysId = '';
       if (groupSysId) {
           var gr = new GlideRecord('sys_user_grmember');
           gr.addQuery('group', groupSysId);
           gr.query();
           if (gr.next()) {
               userSysId = gr.user.toString();
           }
       }
       return userSysId;
   }
});

Onchange client script : on change of group variable

function onChange(control, oldValue, newValue, isLoading) {
   if (isLoading || newValue == '') {
       return;
   }
   var ga = new GlideAjax('GetApproverByGroup');
   ga.addParam('sysparm_name', 'getApprover');
   ga.addParam('sysparm_group', newValue);
   ga.getXML(function(response) {
       var approver = response.responseXML.documentElement.getAttribute("answer");
       if (approver) {
           g_form.setValue('approver', approver);
       }
   });
}

[Shivalika]

His userSysId contains space also. There were 2-3 things I corrected - though minor minor. 

And it's working, what's the point of discussing further.

[Ankur Bawiskar]

@Shivalika 

When I compared the scripts shared by @Bindhu1 and yours there is no difference.

I am just curious to know what was the difference which worked for @Bindhu1 so that it helps future community members.