Javascript Date.getTime() returns NaN in internet Explorer 11 only

Question

I have a below JavaScript function which returns time from the full date.

function f() {
  var monthNames = ["Jan", "Feb", "Mar", "Apr", "May", "Jun",
    "Jul", "Aug", "Sept", "Oct", "Nov", "Dec"
  ];
  d = new Date();
  var utcOffset = -6;
  var utc = d.getTime() + (d.getTimezoneOffset() * 60000);
  var localDate = new Date(utc + (3600000 * (utcOffset + 1)));
  var fullDate = localDate.getDate() + ' ' + monthNames[localDate.getMonth()] + ' ' + localDate.getFullYear() + ' ' + localDate.toLocaleTimeString();
  var now = new Date(fullDate).getTime();
  return now;
}

In all browsers it returns expected output but not for Internet Explorer 11, as it returns NaN.

Please suggest changes to get the expected output.