Advanced reference qualifier not working undefined is not a function

[tdh o2]

Attempting to call a script include from an advanced reference qualifier that queries a table using the value of a string field on the form. Zip field, string, 5 digits. County field, references table that contains all counties in a state and their corresponding zip codes.  Reference qualifier should return all counties associated with the Zip in the string field  or "Out of state" (which is also a record in the counties table) if the Zip does not exist in the table. I'm receiving an error in the system logs com.glide.script.RhinoEcmaError: undefined is not a function.  Also is this script correct to return the values correctly?  Also unclear on how to return Out of State.  This is in the customer service scope.

Current reference qualifier: javascript: new TESTAjaxCountyUtil.getCounties(current.zip);

Script include:

var TESTAjaxCountyUtil = Class.create();
TESTAjaxCountyUtil.prototype = {
    initialize: function() {
    },
    
    getCounties: function (zip) {
        var counties = [];
    
        var grMatch = new GlideRecord('u_m2m_zip_counties');
        grMatch.addQuery('u_zip_code',zip);
        grMatch.query();
        while (grMatch.next()) {
            counties.push(grMatch.u_zip_code.sys_id);
                    
        }
        return 'sys_idIN' + counties;
        
    },
    type: 'TESTAjaxCountyUtil'
};

[tdh o2]

I've tried it in the customer service scope as well as in the global scope with a qualifier with the same result.