Format the relative date

Write a function formatDate(date) that should format date as follows:

If since date passed less than 1 second, then "right now".
Otherwise, if since date passed less than 1 minute, then "n sec. ago".
Otherwise, if less than an hour, then "m min. ago".
Otherwise, the full date in the format "DD.MM.YY HH:mm". That is: "day.month.year hours:minutes", all in 2-digit format, e.g. 31.12.16 10:00.

For instance:

          alert( formatDate(new Date(new Date - 1)) ); // "right now"

alert( formatDate(new Date(new Date - 30 * 1000)) ); // "30 sec. ago"

alert( formatDate(new Date(new Date - 5 * 60 * 1000)) ); // "5 min. ago"

// yesterday's date like 31.12.16 20:00
alert( formatDate(new Date(new Date - 86400 * 1000)) );

Open a sandbox with tests.

To get the time from date till now – let’s substract the dates.

function formatDate(date) {
  let diff = new Date() - date; // the difference in milliseconds

  if (diff < 1000) { // less than 1 second
    return 'right now';
  }

  let sec = Math.floor(diff / 1000); // convert diff to seconds

  if (sec < 60) {
    return sec + ' sec. ago';
  }

  let min = Math.floor(diff / 60000); // convert diff to minutes
  if (min < 60) {
    return min + ' min. ago';
  }

  // format the date
  // add leading zeroes to single-digit day/month/hours/minutes
  let d = date;
  d = [
    '0' + d.getDate(),
    '0' + (d.getMonth() + 1),
    '' + d.getFullYear(),
    '0' + d.getHours(),
    '0' + d.getMinutes()
  ].map(component => component.slice(-2)); // take last 2 digits of every component

  // join the components into date
  return d.slice(0, 3).join('.') + ' ' + d.slice(3).join(':');
}

alert( formatDate(new Date(new Date - 1)) ); // "right now"

alert( formatDate(new Date(new Date - 30 * 1000)) ); // "30 sec. ago"

alert( formatDate(new Date(new Date - 5 * 60 * 1000)) ); // "5 min. ago"

// yesterday's date like 31.12.2016 20:00
alert( formatDate(new Date(new Date - 86400 * 1000)) );

Alternative solution:

function formatDate(date) {
  let dayOfMonth = date.getDate();
  let month = date.getMonth() + 1;
  let year = date.getFullYear();
  let hour = date.getHours();
  let minutes = date.getMinutes();
  let diffMs = new Date() - date;
  let diffSec = Math.round(diffMs / 1000);
  let diffMin = diffSec / 60;
  let diffHour = diffMin / 60;

  // formatting
  year = year.toString().slice(-2);
  month = month < 10 ? '0' + month : month;
  dayOfMonth = dayOfMonth < 10 ? '0' + dayOfMonth : dayOfMonth;
  hour = hour < 10 ? '0' + hour : hour;
  minutes = minutes < 10 ? '0' + minutes : minutes;

  if (diffSec < 1) {
    return 'right now';
  } else if (diffMin < 1) {
    return `${diffSec} sec. ago`
  } else if (diffHour < 1) {
    return `${diffMin} min. ago`
  } else {
    return `${dayOfMonth}.${month}.${year} ${hour}:${minutes}`
  }
}

Open the solution with tests in a sandbox.