How to get Month Name from date

var dateOb = new Date("12/08/2015");
var lang = "en-us";

//If you want month name in long string like : March
var monthInLongStr = dateOb.toLocaleString(lang, { month: "long" });
alert(monthInLongStr );

//If you want month name in short string like : Mar
var monthInShortStr = dateOb.toLocaleString(lang, { month: "short" });
alert(monthInShortStr );