On Change Client Script :

function onChange(control, oldValue, newValue, isLoading) {
if (isLoading || newValue == '') {
return;
}

var ga1 = new GlideAjax('global.itbmDataPatchCatalogUtils');
ga1.addParam('sysparm_name', 'populateMRVS1');
ga1.addParam('p_selected_module', g_form.getDisplayValue('select_a_module'));
ga1.addParam('p_project_number', g_form.getDisplayValue('select_a_project'));
ga1.addParam('p_project_field', g_form.getDisplayValue('select_a_field_from_project'));
ga1.addParam('p_project_portfolio_field_value', g_form.getDisplayValue('new_project_portfolio'));
ga1.getXML(parseData);

function parseData(response) {
var answer = response.responseXML.documentElement.getAttribute("answer");
alert(answer);
g_form.setValue('data_for_update', answer);


// var mvrs = JSON.parse(g_form.getValue('data_for_update'));
// if (mrvs != '') {
// g_form.setValue('data_for_update', answer);
// } else {
// for (var i = 0; i <= 10; i++) {
// var tempObj = {};
// tempObj.answer = i + 4;
// mvrs.push(answer);
// }
// g_form.setValue('data_for_update', JSON.stringify(mvrs));
// }



}
}

Script Include :

var itbmDataPatchCatalogUtils = Class.create();
itbmDataPatchCatalogUtils.prototype = Object.extendsObject(AbstractAjaxProcessor, {

populateMRVS1: function() {
var dataArr = [];
var p1 = this.getParameter('p_selected_module');
var p2 = this.getParameter('p_project_number');
var p3 = this.getParameter('p_project_field');
var p4 = this.getParameter('p_project_portfolio_field_value');
dataArr.push({
"itbm_module": p1.toString(),
"record": p2.toString(),
"field_name": p3.toString(),
"new_value": p4.toString()
});
return JSON.stringify(dataArr);
},

type: 'itbmDataPatchCatalogUtils'
});