Resolved! I want to return Array from script include and use it in the glide ajax of client script what's wrong in my approach...
client script var ga = new GlideAjax('TASK_return_array_SI'); ga.addParam('sysparm_name', 'getCallerDetails'); ga.addParam('sysparm_inc', g_form.getValue('caller_id')); ga.getXML(showDetails); function showDetails(response) { ...