How is it done, a timer in the tab title?

Question

JavaScript

I click on start with keyboard control and if you look at the shortcut of the browser tab, then there is a countdown.
https://htdt.github.io/digital_trip/

Answer 1

Update HTML tag every second with JavaScript.

Answer 2

Feature from this site...

DT.Game.prototype.updateTimer = function (dtime) {
        var sec, min;
        this.timer += dtime;
        sec = Math.floor(this.timer);
        if (sec > Math.floor(this.timer - dtime) ) {
            min = Math.floor(sec / 60);
            sec = sec % 60;
            sec = sec < 10 ? '0' + sec.toString() : sec;
            DT.$title.html(min + ':' + sec + ' in digital trip');
        }
    };

Everything can be viewed in the console, tab Sources

Answer 3

<title> tag

Answer 4

const BASE_TITLE = 'bla bla';
function onProgress(persent) {
  document.title = `${persent}% ${BASE_TITLE}`;
}