Humanize dates in vanilla JavaScript

fancydate.js

console.log(fancyDate(556095600000))
// August 16th, 1987

function fancyDate(input) {

  var input = new Date(input)
  var monthNames = ["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"]
  var monthName = monthNames[input.getMonth()]
  var day = input.getDate()

  if (day > 3 && day < 21) {
    date = day + "th" 
  } else {
    switch (day % 10) {
      case 1:
        date = day + "st"
        break;
      case 2:
        date = day + "nd"
        break;
      case 3:
        date = day + "rd"
        break;
      default:
        date = day + "th"
        break;
    }  
  }

  var year = input.getFullYear()
  return monthName + " " + date + ", " + year
}