JSFiddle - React, Tailwind, and code Playground

JavaScript

var unavailableDates = ["31-5-2015", "1-6-2014", "2-6-2014", "3-6-2014", "26-5-2014", "27-5-2014", "28-5-2014", "29-5-2014"];
function SortByName(a, b){
   var amyDate = a.split("-");
   var aNewDate=new Date(amyDate[1]+","+amyDate[0]+","+amyDate[2]).getTime();
   var bmyDate = b.split("-");
   var bNewDate=new Date(bmyDate[1]+","+bmyDate[0]+","+bmyDate[2]).getTime();
   return ((aNewDate < bNewDate) ? -1 : ((aNewDate > bNewDate) ? 1 : 0));
}
alert(JSON.stringify(unavailableDates.sort(SortByName)));