How to get previous value of calender before edit the value of calendar.

I have a checkbox in each row of table.Now I checked two row and change the date of one row then both rows are updated with new value.But I want to get the old date of all checked row.

How can I get old date of all checked row.

Here is my running code.
Here is my snippet
http://webix.com/snippet/6d3b296c

Please help me.

Within each or iterator, data item is stored as obj, so you can get the original value before applying updateItem