JavaScript 定时器和 sessionStorage

Question

我有以下问题。我有一个计时器函数，它需要一个参数，即秒数。直接通过的话，就可以正常工作，没有任何缺陷。但是，出于多种原因，我需要使用 sessionStorage，并且当我在将变量传递给计时器函数之前从 sessionStorage 检索变量时，它会乘以参数中传递的秒数的 10 倍。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

窗口存储保存字符串。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);

  }