var month = "May";
            var m;
            switch(month) {
                case "January":
                    m = 0;
                    break;
                case "February":
                    m = 1;
                    break;
                case "March":
                    m = 2;
                    break;
                case "April":
                    m = 3;
                    break;
                case "May":
                    m = 4;
                    break;
                case "June":
                    m = 5;
                    break;
                case "July":
                    m = 6;
                    break;
                case "August":
                    m = 7;
                    break;
                case "September":
                    m = 8;
                    break;
                case "October":
                    m = 9;
                    break;
                case "November":
                    m = 10;
                    break;
                case "December":
                    m = 11;
                    break;
                default:
                //
            }
        console.log(m);

var months = ["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"];

var m = months.indexOf('May');  // 4

var monthnames = ['Jan', 'Feb', 'Mar', 'Apr']; // etc
var month = 'Mar';
var monthno = monthnames.indexOf(month);
console.log(monthno) // 2

function getMonthFromString(monthName){

   var d = Date.parse(mon + "1, 2000");
   if( !isNaN(d) )
    {
      return new Date(d).getMonth();
   }
   return -1;
}