UTCDate(ms) - convert 1363358559454 to "March 15, 2013 at 7:42:39 AM"

utc-date-to-locale-date-string.js

// 16 July 2019
export { UTCDate };

/**
 * @function UTCDate accepts a datetime number or string in milliseconds since
 * 1 January 1970 UTC and returns a formatted human-readable date string.
 *
 * Given: UTCDate(1363358559454)
 * Returns: "March 15, 2013 at 7:42:39 AM"
 *
 * NOTE: timestamps may need to be saved as GMT (+0) if we want to convert them
 * to offest timezone dates...
 *
 * @param {number|string} ms - milliseconds since 1 January 1970 UTC.
 * @returns {string}
 */

function UTCDate(ms) {
  var date = new Date(ms);
  
  var utc = Date.UTC(
    date.getUTCFullYear(),
    date.getUTCMonth(),
    date.getUTCDate(),
    date.getUTCHours(),
    date.getUTCMinutes(),
    date.getUTCSeconds()
  );
  
  var event = new Date(utc);
  
  // Not sure if we need this offset from GMT timezone...
  // event.setTime( event.getTime() + event.getTimezoneOffset() * 60 * 1000 );

  var options = {
    year: 'numeric',
    month: 'long',
    day: '2-digit',
    hour: '2-digit',
    minute: '2-digit',
    second: '2-digit'
  };

  // Create locale string, split it after the year, join it with ' at '.
  var ls = event.toLocaleDateString("default", options);
  var fy = String(date.getUTCFullYear());
  var sp = ls.indexOf(fy)  + fy.length ;
  
  return [
    ls.substring(0, sp),
    'at',
    ls.substring(sp + 2)
  ].join(' ');
}

/* test it out */

var tests = [
  1363358559454, // March 15, 2013 at 7:42:39 AM
  Date.now(),
  Date.parse( new Date(2004, 01, 29, 1, 2, 3) )
];

var results = tests.map(ms => {  
  return { ms: ms, utc: UTCDate(ms) };
});

var report = JSON.stringify(results, null, 2);

console.log(report);

/*
 [
  {
    "ms": 1363358559454,
    "utc": "March 15, 2013 at 7:42:39 AM"
  },
  {
    "ms": 1563311835142,
    "utc": "July 16, 2019 at 2:17:15 PM"
  },
  {
    "ms": 1078045323000,
    "utc": "February 29, 2004 at 1:02:03 AM"
  }
]
*/