Display text when timer reaches 0s, and add 0 before 1-9s

javascript

I want to display some text once the timer goes to 0:00, and when the timer is anywhere in between 1-9s, I want to display a 0 in front of the seconds, e.g. 1:04 instead of 1: 4. How would I do this?

const timeSpan = document.getElementById('timer');
var sec = 600 / 60;
const mins = sec;
const now = new Date().getTime();
const deadline = mins * 60 * 1000 + now;


setInterval(() => {
  var currentTime = new Date().getTime();
  var distance = deadline - currentTime;
  var minutes = Math.floor((distance % (1000 * 60 * 60)) / (1000 * 60));
  var seconds = Math.floor((distance % (1000 * 60)) / 1000);


  timeSpan.innerHTML = minutes + ':' + seconds;
  
}, 500)

You can:

Check minutes+seconds <= 0. If this is true, the count down reached 0. You can use this condition to output a custom string.
Get a the id of the timer from the call to setInterval and use it to stop the timer when the delay is zero.
Format the output by replacing single digits with double digits, using a regular expression. There are many other ways to do this.

const timeSpan = document.getElementById('timer');
const mins = 6 / 60; // For the demo I shortened the deadline
const now = new Date().getTime();
const deadline = mins * 60 * 1000 + now;

// Get the timer identifier
let timer = setInterval(() => {
  var currentTime = new Date().getTime();
  var distance = deadline - currentTime;
  var minutes = Math.floor((distance % (1000 * 60 * 60)) / (1000 * 60));
  var seconds = Math.floor((distance % (1000 * 60)) / 1000);

  if (minutes+seconds <= 0) { // The delay is 0
      timeSpan.innerHTML = "You can claim points";
      clearInterval(timer); // Stop the timer
  } else {
      // Replace single digits with double digits
      timeSpan.innerHTML = (minutes + ':' + seconds).replace(/\b\d\b/g, "0$&");
  }
}, 500);