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Jun 24, 2016 am 11:17 AM

一setTimeout函数和setInterval函数的语法以及应用

1.setTimeout函数

定义和用法:setTimeout()方法用于在指定的毫秒数后调用函数或计算表达式。　　

语法:setTimeout(code,millisec);

参数：

code （必需）：要调用的函数后要执行的 JavaScript 代码串。　　

millisec（必需）：在执行代码前需等待的毫秒数。　　

注意：

setTimeout() 只执行 code 一次。如果要多次调用，请使用 setInterval() 或者让 code 自身再次调用 setTimeout()。

返回值

一个可以传递给 Window.clearTimeout() 从而取消对 code 的周期性执行的值。

既然setTimeout是一个定时器函数，那么就有一个一个函数来清理定时器，那我们就用到了clearTimeout函数。

clearTimeout（setTimeout（）返回的ID值）；

2.setInterval定义

setInterval() 方法可按照指定的周期（以毫秒计）来调用函数或计算表达式。

setInterval() 方法会不停地调用函数，直到 clearInterval() 被调用或窗口被关闭。由 setInterval() 返回的 ID 值可用作 clearInterval() 方法的参数。

语法

setInterval(code,millisec[,"lang"])；

参数code必需。要调用的函数或要执行的代码串。

millisec必须。周期性执行或调用 code 之间的时间间隔，以毫秒计

返回值

一个可以传递给 Window.clearInterval() 从而取消对 code 的周期性执行的值。

既然setTimeout是一个定时器函数，那么就有一个一个函数来清理定时器，那我们就用到了clearInterval()函数。

clearInterval()（setInterval（）返回的ID值）；

eg.

1.倒计时的效果

<!DOCTYPE html><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>    <title>倒计时效果</title>    <script type="text/ecmascript">        //使用js方式实现倒计时效果        var t1;        window.onload = function () {                      //01定位到开始按钮返回一个dom对象            var btns = document.getElementById('btnStart');            //02.给开始按钮注册单击事件            btns.onclick = function () {                //执行ssetInerval函数第一个参数要定时执行的函数，第二个参数该函数每个多少毫秒执行一次                t1= setInterval(start, 1000);            }            //03定位到停止按钮返回一个dom对象            var btnst = document.getElementById('btnStop');            btnst.onclick = function () {               clearInterval(t1);            }        }       //要隔1秒执行的函数        function start() {            //01.获取div中的文本赋值给一个变量            var divdom = document.getElementById('msg');            var divnum = divdom.innerText;            //判断divnum的值是否为0            if (divnum > 0) {                divnum--;                //把减过的值重新赋值给divnum                divdom.innerText = divnum;            }        }    </script></head><body>    <input type="button" id="btnStart" value="开始"  />    <input type="button" id="btnStop"  value="停止" /><br />    <div id="msg">10</div></body></html>

2.图片的切换

<!DOCTYPE html><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>    <title></title>    <script type="text/javascript">        var count = 1;//定义初始变量默认为第一张图片        window.onload = function () {           //使用定时器函数每隔一秒定义执行一次show函数            setInterval(show,1000);        }        //要执行的函数        function show() {            //如果图片到达最后一张（5张），就将下一张显示的图片改为第一张，如果没有到达最后一张就将显示下一张图片            if (count > 5) {                count = 1;            }            else {                count++;            }            //获取id为myimg的dom对象            var dom = document.getElementById("myimg");            //改变img标签的src属性指向，改变图片            dom.src = "image/"+count+".jpg"        }    </script></head><body>    <img src="/static/imghwm/default1.png"  data-src="image/1.jpg"  class="lazy" alt="Alternate Text"    style="max-width:90%" height="200px" id="myimg" /></body></html>

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