javascript 计时器和会话存储

Question

我有以下问题。我有一个计时器功能，它需要一个参数，即秒数。直接通过它时，它可以正常工作。但是，由于多种原因我需要使用 sessionStorage，当我在将变量传递给计时器函数之前从 sessionStorage 检索变量时，它乘以 10 传递给参数的秒数。我不明白为什么它有这种行为。我写了一个最小的例子来说明我的问题：

function countdown(time_p) {
  var saved_countdown = sessionStorage.getItem('saved_countdown');
  var time;

  if (saved_countdown == null) {
    // Set the time we're counting down to using the time allowed
    var new_countdown = new Date().getTime() + (time_p + 2) * 1000;
    time = new_countdown;
    sessionStorage.setItem('saved_countdown', new_countdown);
  } else {
    time = saved_countdown;
  }
  // Update the count down every 1 second
  var x = setInterval(() => {

    // Get today's date and time
    var now = new Date().getTime();

    // Find the distance between now and the allowed time
    var distance = time - now;

    // Time counter
    var counter = Math.floor(distance / 1000);

    // Output the result in an element with id="demo"
    document.getElementById("demo").innerHTML = counter + " s";

    // If the count down is over, write some text 
    if (counter <= 0) {
      clearInterval(x);
      sessionStorage.removeItem('saved_countdown');
      sessionStorage.removeItem('max_time');
      document.getElementById("demo").innerHTML = "EXPIRED";
    }
  }, 1000);
}

$("#confirm_settings").click(function() {
  var time = $("#time").val();
  console.log("time entered" + time);
  sessionStorage.setItem('max_time', time);
  time = sessionStorage.getItem('max_time'); // multiply the time entered by 10 ...
  // time = 42; // works well
  console.log("time = " + time);
  countdown(time);
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.3/jquery.min.js">
</script>
<p id="demo"> </p>
<label for "time"> Time limit :</label>
<input type="text" id="time" placeholder="enter a duration (s)"> <br>
<button type="button" id="confirm_settings">OK</button>

Answer 1

window storage 保存字符串。您需要将它们转换为整数：

function countdown(time_p) {
  var time = sessionStorage.getItem('saved_countdown');

  if (time) {
    time = +time; // cast the string to number
  }
  else {
    // Set the time we're counting down to using the time allowed
    var new_countdown = new Date().getTime() + (time_p + 2) * 1000;
    time = new_countdown;
    sessionStorage.setItem('saved_countdown', new_countdown);
  }

javascript 计时器和会话存储

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