This article will help you to export the full name of the last month. 

Step-by-step guide

Last month was …

%{var monthNames = ["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"]; var dt = new Date(); dt.setMonth(dt.getMonth() - 1); monthNames[dt.getMonth()]}

Link for related documentation

https://confluence.xpand-it.com/display/public/XPORTER/JavaScript