[closed] how to show the difference between current date and due date through script based calculated value?

I am using RTC3013 and want to show the difference between current date and due date in the task.
I followed the instruction in the below article to set the ccm/admin first.
Then create script as below

dojo.provide("ibm.example.workitems.providers.CalculatedValueSkeleton");
dojo.require("com.ibm.team.workitem.api.common.WorkItemAttributes");
dojo.require("dojo.date");
dojo.require("dojo.date.stamp");

(function() {
var WorkItemAttributes= com.ibm.team.workitem.api.common.WorkItemAttributes;

dojo.declare("ibm.example.workitems.providers.CalculatedValueSkeleton", null, {

    getValue: function(attributeId, workItem, configuration) {


    var dueDate= dojo.date.stamp.fromISOString(workItem.getValue(WorkItemAttributes.DUE_DATE));
        var currentDate= new Date();
        var dayDiff= dojo.date.difference(dueDate,currentDate, "day");
        var result = 0;
    if (dayDiff > 0) result=dayDiff;         
    }
        return result;
    }
});
})();

In Eclipse client, add new calculated value to customized attribute and point to the above js file
Create a new attribute and use the new created calculated value and set it as dependent on duedate.
Add the new attribute to task presentation.
When I create a new task, I can see the new attribute is there, but after I select a due date and save the WI, nothing happens to the attribute(blank)

I am wondering how I can achieve that: whether something is wrong in my script or I missed anything?
Would appreciate if anyone can comment on what's wrong. Thank you very much.