How do I get in JS the values shown in the “Allocated Supply” dialog?

Hello,
My record is sales order.
In UI if I go to “Items” subtab and click on the number in “Allocated Supply” column then the “Allocated Supply” dialog will appear.
If I need read information about items in JS, I use code like following:

context.newRecord.getSublistValue({sublistId: ‘item’, fieldId: ‘quantityallocated’, line: i})
(where “i” is some counter variable).

Please advice how do I get in JS the values shown in the “Allocated Supply” dialog?
Is this some other sublist in “Sales Order” record?