• javascript 定时器


     js 的定时器,经常会用到,用来做定时的,有两种定时器:

    1.定时器的设置:

    1.1. setTimeout(fn,time) :   只执行一次,执行完就不再执行了

    1.2. setInterval(fn,time):  循环执行,每进过time时间,自动执行fn ,直到清除定时器为止

    2.定时器的清除:

    清除定时器,也有两种方法:

    2.1  clearInterval(timer)  ,清除定时器timer,在这里,timer是定时器的名称

    2.2 clearTimeout(timer ) ,清除定时器timer,在这里,timer是定时器的名称

     1 <!DOCTYPE html>
     2 <html lang="en">
     3 <head>
     4     <meta charset="UTF-8">
     5     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     6     <meta http-equiv="X-UA-Compatible" content="ie=edge">
     7     <script src="https://code.jquery.com/jquery-3.1.1.min.js"></script>
     8     <title>Document</title>
     9     <style>
    10         div {
    11             position: relative;
    12             margin: 100px auto;
    13             width: 300px;
    14             height: 100px;
    15             background: #ccc;
    16         }
    17         span {
    18             margin: 20px auto;
    19             position: relative;
    20             display: inline-block;
    21             width: 100%;
    22             background: #290;
    23             text-align: center;
    24         }
    25     </style>
    26     <script>
    27         $(function() {
    28             var jishi = 10;
    29             var timer = null;
    30             function change_span() {
    31                 if (jishi > 0) {
    32                     jishi--;
    33                     $("#box span").html("现在计时器为:" + jishi);
    34                 }
    35             }
    36             timer = setInterval(change_span, 1000);
    37         });
    38     </script>
    39 </head>
    40 <body>
    41     <div class="box" id="box">
    42         <span>
    43         </span>
    44     </div>
    45 </body>
    46 </html>

    运行结果:

    改成setTimeout之后:

     1  <script>
     2         $(function() {
     3             var jishi = 10;
     4             var timer1 = timer2 = null;
     5 
     6             function change_span() {
     7                 if (jishi > 0) {
     8                     jishi--;
     9                     $("#box span").html("现在计时器为:" + jishi);
    10                 }
    11             }
    12             // timer1 = setInterval(change_span, 1000);
    13             timer2 = setTimeout(change_span, 1000);
    14         });
    15     </script>

    运行结果:

    差异: 

    setInterval 无限次循环执行,直到清除定时器;

    setTimeout 只执行一次,执行完之后,定时器停止执行;

    3. 清除定时器:

     1 <!DOCTYPE html>
     2 <html lang="en">
     3 <head>
     4     <meta charset="UTF-8">
     5     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     6     <meta http-equiv="X-UA-Compatible" content="ie=edge">
     7     <script src="https://code.jquery.com/jquery-3.1.1.min.js"></script>
     8     <title>Document</title>
     9     <style>
    10         div {
    11             position: relative;
    12             margin: 100px auto;
    13             width: 300px;
    14             height: 100px;
    15             background: #ccc;
    16         }
    17         span {
    18             margin: 20px auto;
    19             position: relative;
    20             display: inline-block;
    21             width: 100%;
    22             background: #290;
    23             text-align: center;
    24         }
    25     </style>
    26     <script>
    27         $(function() {
    28             var jishi = 10;
    29             var timer1 = timer2 = null;
    30             function change_span() {
    31                 if (jishi > 0) {
    32                     jishi--;
    33                     $("#box span").html("现在计时器为:" + jishi);
    34                 }
    35             }
    36             timer1 = setInterval(change_span, 1000);
    37             $("#btn").on('click', function() {
    38                 clearInterval(timer1);
    39             });
    40         });
    41     </script>
    42 </head>
    43 <body>
    44     <div class="box" id="box">
    45         <span>
    46                 </span>
    47         <input type="button" value="点击清除定时器" id="btn">
    48     </div>
    49 </body>
    50 </html>

    运行结果:在定时器为5 时,点击清除按钮,然后定时器就停止了

    4. 把clearInterval 改成clearTimeout,

     1 <script>
     2         $(function() {
     3             var jishi = 10;
     4             var timer1 = timer2 = null;
     5 
     6             function change_span() {
     7                 if (jishi > 0) {
     8                     jishi--;
     9                     $("#box span").html("现在计时器为:" + jishi);
    10                 }
    11             }
    12             timer1 = setInterval(change_span, 1000);
    13             $("#btn").on('click', function() {
    14                 // clearInterval(timer1);
    15                 clearTimeout(timer1);
    16             });
    17 
    18         });
    19     </script>

    运行结果也是一样的:在定时器为7 的时候点击清除按钮

    备注:定时器,不论是设置定时器,还是清除定时器,都是window 下面的方法,挂载在 window 对象上面;另外设置定时器的第二个参数,时间单位为毫秒(ms),例如setInterval(fn,1000) ,指的是1000ms 运行一次fn ,循环运行

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  • 原文地址:https://www.cnblogs.com/huanying2015/p/8541782.html
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