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How to use setTimeout() in JavaScript to set a timer

青灯夜游

Dec 10, 2018 pm 02:33 PM

javascript

In JavaScript, by setting the function to be called or the code string parameters to be executed, and the delay time parameter to the setTimeout() method, a simple timer can be set by calling the setTimeout() method.

How to use setTimeout() in JavaScript to set a timer

In JS, some native methods are provided to execute a certain piece of code after a set time interval; the setTimeout() method sets a one-time timer , is triggered only once after the specified delay time. Let's take a look at how the setTimeout() method sets the timer.

setTimeout() method

setTimeout(): Set a one-time timer and call a function or calculation expression after the specified number of milliseconds ; Will execute the expression once after delaying the specified time during loading, and only execute it once. [Recommended related video tutorials: JavaScript Tutorial]

Syntax:

setInterval(code,millisec,lang);

Parameter description:

code: Required parameters, indicating the function that needs to be called or a string of code to be executed.

millisec: A required parameter, indicating the time interval before periodic execution or calling "code parameter", measured in milliseconds (1s=1000ms).

lang optional parameter.

Example of setTimeout() method:

html code:

<p>点击按钮，在等待 3 秒后弹出 "Hello"。</p>
<button onclick="myFunction()">点我</button>

js code:

function myFunction()
{
	setTimeout(function(){alert("Hello")},3000);
}

Rendering ：

How to use setTimeout() in JavaScript to set a timer

setTimeout() sets an infinite loop timer

You can also use the setTimeout() method To implement an infinite loop timer, we need to write a function to call itself. At this time, the setTimeout() method will loop infinitely. If you want to stop the timer, you need to use the clearTimeout() method.

clearTimeout() method

clearTimeout(): used to cancel the timer set by setTimeout(), used when setting setTimeout() for an infinite loop.

Syntax:

clearTimeout(id_of_setTimeout);

Parameter description:

id_of_setTimeout: Represents the ID value returned by setTimeout().

Note: This value identifies the delayed call function or delayed execution code string to be canceled;

Combined example of setTimeout() method and clearTimeout() method

<!DOCTYPE HTML>
<html>
<head>
<script type="text/javascript">
  var num=0,i;
  function timedCount(){
    document.getElementById(&#39;txt&#39;).value=num;
    num=num+1;
    i=setTimeout(timedCount,1000);
  }
    setTimeout(timedCount,1000);
  function stopCount(){
    clearTimeout(i);
  }
</script>
</head>
<body>
  <form>
    <input type="text" id="txt">
    <input type="button" value="Stop" onClick="stopCount()">
  </form>
</body>
</html>

Rendering:

How to use setTimeout() in JavaScript to set a timer

#It can be seen that the timer set by setTimeout() is looping infinitely at the beginning, making the number in the input box It continues to increase. When the Stop button is pressed, the clearTimeout() method will be called to stop the setTimeout() timer. The number will stop increasing and remain at the number 11.

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