How to calculate the exact difference between dates in years?

Question

JavaScript

How to determine the exact difference in years between the current date and the date in the format "0000-00-00 00:00:00". In PHP this is easily solved:

DateTime::createFromFormat("Y-m-d H:i:s", '2014-09-12 00:00:00')
->diff(new DateTime('now'))
->y;

Is there a similar elegant solution in Java Script?

Answer 1

Final code. The input is a date in the format '0000-00-00 00:00:00', the output is the number of full years from the current date:

function age_count(date) {
    // now
    var now = new Date();
    now.setMinutes(now.getMinutes() - now.getTimezoneOffset());
    now = now.toISOString().substr(0, 19).replace('T',' ');
    // calculate
    var age = now.substr(0, 4) - date.substr(0, 4);
    if(now.substr(5) < date.substr(5)) --age;
    // output
    return age;
}

PS If anyone knows how to more briefly bring the current date to the format '0000-00-00 00:00:00' - please write in the comments.

Answer 2

var date1 = '2014-09-12 12:34:56';
var date2 = '2017-09-12 12:34:56';
if(date1.substr(5) == date2.substr(5) {
  alert('Господин программный архитектор, у вас день рождения наступило!');
} else {
  var years = date2.substr(0, 4) - date1.substr(0, 4);
  if(date2.substr(5) < date1.substr(5)) {
    --years;
  }
  alert('Вам таки ' + years + ' полных лет, а толку?');
}

Answer 3

We create two Date objects, birthday and now. To ensure that a date object is correctly obtained from a text string, you must first convert it to ISO 8601 format - the simplest is to replace the space with the letter "T". But such a date will be in the UTC time zone, you need to adjust it by adding minutes from getTimezoneOffset(). For example, the date "2014-09-12 00:00:00" Moscow time is September 11, 21:00 UTC. When comparing from "now", we will take UTC time - getUTCMonth(), etc.
Having received two dates, we compare their months, dates. If you need more accuracy, then also hours, minutes, seconds:

var sqlDT = "2014-09-12 00:00:00";
var BD = new Date( sqlDT.replace(' ','T'));
var Now = new Date();
BD.setMinutes( BD.getMinutes() + Now.getTimezoneOffset()); // в UTC

if( BD.getMonth() === Now.getUTCMonth()
  && BD.getDate() === Now.getUTCDate()
) {
  // ура! День рождения!
}

Ps An alternative option is to connect a hefty library for working with dates and times -  MomentJS , and find suitable methods in it.