GlideAjax returning null Date Time value

[MBarrott]

I've created a onChange client script which will ultimately call a GlideAjax script include function. 

The end goal is that if someone selects a change request ticket for the reference field in my demand task form, this script will retrieve the planned end date (end_date) from the change_request table and automatically populate the due_date field. 

It appears that regardless of what I try to retrieve from the Script Include I'm consistently getting null back from the callback function.

CLIENT SCRIPT:

function onChange(control, oldValue, newValue, isLoading, isTemplate) {
   if (isLoading || newValue === '') 
   {
      return;
   }
	
	//Type appropriate comment here, and begin script below
	if(g_form.getDisplayBox('u_change_request').value != '')
	{
		alert('entered if');
		alert('passing over: ' + g_form.getDisplayBox('u_change_request').value);
		var value = g_form.getDisplayBox('u_change_request').value;
		
		var chgAjax = new GlideAjax('ChangeRequestDateFinder');
		chgAjax.addParam('sysparm_name', 'endDateFinder');
		chgAjax.addParam('sysparm_ticket', g_form.getDisplayBox('u_change_request').value);
		chgAjax.getXML(myCallBack);	
	}
}

function myCallBack(response)
{   //the argument 'response' is automatically provided when the callback funciton is called by the system.
	//Dig out the 'answer' attribute, which is what the function returns. 
	alert('entered callback');
	var endDate = response.responseXML.documentElement.getAttribute('answer');  
	alert('endDate value is: ' + endDate);
	//g_form.setValue('due_date', endDate);
}

SCRIPT INCLUDE:

var ChangeRequestDateFinder = Class.create();
ChangeRequestDateFinder.prototype = Object.extendsObject(AbstractAjaxProcessor, 
{
	endDateFinder: function() 
	{
		var ticketNum = this.getParameter('sysparm_ticket');
		var gr = new GlideRecord('change_request');
		gr.addQuery(number, 'CHG20002482');
		gr.query();
		var endDate = gr.getValue('end_date');		
		return endDate;
    }
});

[MBarrott]

Hi @Samiksha Gunjat 

Thank you for this. I had actually fixed the script myself eventually but your solution was near identical to what I ended up doing. Accepted as solution.