定义和用法

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"])
参数描述
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。

实例

<html>
<body>
<input type="text" id="clock" size="35" />
<script language=javascript>
var int=self.setInterval("clock()",50)
function clock()
  {
  var t=new Date()
  document.getElementById("clock").value=t
  }
</script>
</form>
<button onclick="int=window.clearInterval(int)">
Stop interval</button>
</body>
</html>


现附上实时显示当前系统时间的代码：
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
        <title></title>
</head>


<body>
        <form id="form1" runat="server">
        <div>
        <div id="idTime"> </div>
        <script>
                /*date*/
                function GetTime() {
                        var d = new Date(), sResult = d.getYear() + "年 " + (d.getMonth() + 1) + "月 " + d.getDate() + "日 星期";
                        switch (d.getDay()) {
                                case 0:
                                        sResult += "天";
                                        break;
                                case 1:
                                        sResult += "一";
                                        break;
                                case 2:
                                        sResult += "二";
                                        break;
                                case 3:
                                        sResult += "三";
                                        break;
                                case 4:
                                        sResult += "四";
                                        break;
                                case 5:
                                        sResult += "五";
                                        break;
                                case 6:
                                        sResult += "六";
                                        break;
                        }
                        return sResult + " " + Right(("0" + d.getHours()), 2) + ":" + Right(("0" + d.getMinutes()), 2) + ":" + Right(("0" + d.getSeconds()), 2);
                }
                function Right(string, length) { return string.substring(string.length - length); }
                /*日期*/
                var oTime = document.getElementById("idTime");
                oTime.innerHTML = GetTime();
                setInterval(function() { oTime.innerHTML = GetTime(); }, 1000)
</script>
        </div>
        </form>
</body>
</html>