scripting issue

[SLeelaRaR]

Hi ,Here I wrote the  server side & client script to auto populate the caller values  when caller is changed ., but i am not getting perfect result ., so please correct my code to achieve the result.
----script include ------

var PopulateCallerData = Class.create();

PopulateCallerData.prototype = Object.extendsObject(AbstractAjaxProcessor, {

    getcaller: function() {

        var callerObj = {};

        var gr = new GlideRecord('sys_user');

        gr.addQuery('sys_id', this.getParameter('sysparm_user_id'));

        gr.query();

        if (gr.next()) {

            callerObj.fname = gr.getValue('first_name');

            callerObj.lname = gr.getValue('last_name');

            callerObj.email = gr.getValue('email');

            callerObj.manager = gr.getValue('manager');

        }

        return JSON.stringify(callerObj);

    },

    type: 'PopulateCallerData'

});

------------client script--------------

function onChange(control, oldValue, newValue, isLoading, isTemplate) {

    if (isLoading || newValue === '') {

        return;

    }

    var ga = new GlideAjax('PopulateCallerData');

    ga.addParam('sysparm_name', 'getcaller');

    ga.addParam('sysparm_user_id', g_form.getValue('caller_id'));

    ga.getXMLAnswer(function(response) {

        var result = JSON.parse(response);

        alert(result);

    });

}

I am getting result as [object object] in alert ., in alert I want to get the result.

[SophiaGraham]

Your code looks good! Maybe check GlideRecord for correct parameters?