Design Studio scripting: Adding a button to filter on year to date

This code works in Design Studio, but the date is hardcoded:

TABSTRIP_1.setSelectedTab("TAB_1");

DS_OPPS_WON.setFilterExt("0CRM_EXPEND",">=1/1/2012");

I cannot find SAP javascript functions that work to perform a dynamic YTD filter rather than hardcoding the date.