为什么clearInterval只工作一次?

问题描述

我有这个例子:

<p id="test"></p>

<button onClick="clearInterval(myVar)">Stop time!</button>
<button onClick="setInterval(myTimer, 1000)">Start time!</button>

<script>

var myVar = setInterval(myTimer, 1000);

function myTimer() {
    var d = new Date();
    document.getElementById('test').innerHTML = d.toLocaleTimeString();
}

</script>

当我单击停止时间！"时第一次可以正常运行，但是在我单击开始时间！"之后我不能再停止计时器了.为什么会发生这种情况以及如何解决呢?

When I click "Stop time!" for the first time it works as it should, but after I click "Start time!" I cannot stop timer anymore. Why exactly is this happening and how to fix this?

谢谢.

推荐答案

查看此代码

<button onClick="setInterval(myTimer, 1000)">Start time!</button>

它不起作用，因为您没有将新计时器设置为变量.它不知道应该在此处设置新值.

It does not work because you do not set the new timer to the variable. It does not know the new value should be set there.

不喜欢内联代码，但是可以使用

Not a fan of inline code, but this would work

<button onClick="myVar = setInterval(myTimer, 1000)">Start time!</button>

更好的设计应该是这样的:

A better design would be something like this:

(function() {

  var timer;

  function myTimer() {
    var d = new Date();
    document.getElementById('test').innerHTML = d.toLocaleTimeString();
  }

  function startTimer() {
    stopTimer(); //make sure timer is not already running
    timer = setInterval(myTimer, 1000); //start new timer
  }

  function stopTimer() {
    if (timer) clearInterval(timer);
    timer = null;
  }

  document.getElementById("stop").addEventListener("click", stopTimer);
  document.getElementById("start").addEventListener("click", startTimer);

  startTimer();

}());

<p id="test"></p>

<button id="stop">Stop time!</button>
<button id="start">Start time!</button>

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