How to get server date using JavaScript?

If you are running JavaScript at the client-side, the only way to find the server time is asking the server what is the current time. There is no magic here. You need to make a request to the server.

Options:

1. Use AJAX or Fetch.
2. If the HTML page is rendered in the server, you can write the current time during the page render and send it to client.

Please, note that it is not possible to have a precise time of the server due to network delays, but you can get pretty close using the code from this answer (modified):

var offset = 0;
function calcOffset() {
    var xmlhttp = new XMLHttpRequest();
    xmlhttp.open("GET", "https://stackoverflow.com/", false);
    xmlhttp.send();

    var dateStr = xmlhttp.getResponseHeader('Date');
    var serverTimeMillisGMT = Date.parse(new Date(Date.parse(dateStr)).toUTCString());
    var localMillisUTC = Date.parse(new Date().toUTCString());

    offset = serverTimeMillisGMT -  localMillisUTC;
}

function getServerTime() {
    var date = new Date();

    date.setTime(date.getTime() + offset);

    return date;
}