How to format a JavaScript date

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

var date = new Date();
var day = date.getDate();
var monthIndex = date.getMonth();
var year = date.getFullYear();

console.log(day, monthNames[monthIndex], year);
document.write(day + ' ' + monthNames[monthIndex] + ' ' + year);