How to format a cell's Date in Numbers with JXA

I have a JXA script that converts a customer-supplied spreadsheet (orders) into a format. Everything works except one Date cell. The date is provided in a cell by the customer in their supplied spreadsheet. That cell is formatted with Date-only, no time included. I need to move that date into a different column, but Numbers defaults the Date format to Date & Time. How can I programmatically (with JXA) change the format of that new column (or at least a cell.)