Formate date/time in javascript

format.js

function format(date, format) {
  if (!date || !format) {
    return;
  }
  if (format.toLowerCase() === "short") {
    format = "dd-MM-yyyy";
  }
  if (format.toLowerCase() === "medium") {
    format = "dd-MM-yyyy hh:mm:ss";
  }
  date = new Date(date);
  var o = {
    "M+": date.getMonth() + 1, //month
    "d+": date.getDate(), //day
    "h+": date.getHours(), //hour
    "m+": date.getMinutes(), //minute
    "s+": date.getSeconds(), //second
    "q+": Math.floor((date.getMonth() + 3) / 3), //quarter
    "S": date.getMilliseconds() //millisecond
  };
  if (/(y+)/.test(format)) {
    format = format.replace(
      RegExp.$1,
      (date.getFullYear() + "").substr(4 - RegExp.$1.length)
    );
  }
  for (var k in o)
    if (new RegExp("(" + k + ")").test(format)) {
      format = format.replace(
        RegExp.$1,
        RegExp.$1.length == 1 ?
        o[k] :
        ("00" + o[k]).substr(("" + o[k]).length)
      );
    }
  return format;
}


console.log(format('2018-07-17T09:03:08.819Z', 'yyyy-mm-dd'))
console.log(format('2018-07-17T09:03:08.819Z', 'short'))
console.log(format('2018-07-17T09:03:08.819Z', 'medium'))