How to alert when count down is over

Question

Please help me! I make some simple app for bike renting in local storage. How to alert("Expired") when counter reach zero. When i put alert inside setInterval method, i have repeating alert evry second.

var interval = 5000;

function reset() {
  localStorage.endTime = +new Date + interval;
}

if (!localStorage.endTime) {
  reset();
}

var remaining = localStorage.endTime - new Date;
setInterval(brojanje, 100)

function brojanje() {
  if (remaining > 0) {
    $('#timer').text(Math.floor(remaining / 1000));
  } else {
    return;
  }
}

<div Time remaining: <span id="timer">
  </span>
</div>
<button onclick="reset()">Click me</button>

Answer 1

You need to stop your timer using clearInterval function.

        var interval = setInterval(brojanje, 100);
        function brojanje() {
            if (remaining > 0) {
                $('#timer').text(Math.floor(remaining / 1000));
            } else {
                console.log('Alert and kill timer');
                alert('STOP!');
                clearInterval(interval);
            }
        }

Answer 2

Here's a version I worked on. I removed the use of jquery too.

<script>
  let duration = 5000
  let end_time = 0
  let the_interval

  function reset () {
    end_time = Date.now() + duration
    localStorage.endTime = end_time
  }

  function start_interval () {
    clearInterval(the_interval)

    let timer = document.querySelector("#timer")

    the_interval = setInterval(function () {
      let remaining = end_time - Date.now()
      
      if (remaining <= 0) {
        clearInterval(the_interval)
        return
      }

      timer.textContent = Math.floor(remaining / 1000)
    }, 100)
  }

  window.onload = function () {
    document.querySelector("#reset_button").addEventListener("click", function () {
      reset()
      start_interval()
    })

    end_time = parseInt(localStorage.endTime)

    start_interval()
  }
</script>

<span>Time remaining:</span> <span id="timer"></span></div>
<button id="reset_button">Click me</button>