<script>
var now = new Date();
var ny = Math.floor(now.getTime() / (1000*60*60*24));

var from = new Date(2018,0,1,0,0,0);
var newYear = Math.floor(from.getTime() / (1000*60*60*24));

var total = newYear - ny;

var out = document.getElementById('out').innerHTML = "До Нового Года" + "<span>" + total + "</span>" + "дней";
</script>

//© [url]https://gist.github.com/tomfun/830fa6d8030d16007bbab50a5b21ef97[/url]
  function getNoun(number, one, two, five) {
    let n = Math.abs(number);
    n %= 100;
    if (n >= 5 && n <= 20) {
      return five;
    }
    n %= 10;
    if (n === 1) {
      return one;
    }
    if (n >= 2 && n <= 4) {
      return two;
    }
    return five;
  }

alert(getNoun(20,'день','дня','дней'));