01效果图:

02运用:
- window.setTimeout()刷新
- function()函数
- document.forms():表单
- if条件语句
- window.alert()窗口警示
03、操作代码:
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>无标题文档</title>
</head><body><form name="forms"><div align="left"><input type="text" name="input1" size="10"><!--建立一个表单--><script>var sec=0;var min=0;var hou=0;flag=0;//后面用来定点1分钟弹出提醒idt=window.setTimeout("update();",1000);function update(){sec++;if(sec==60){sec=0;min+=1;}if(min==60){min=0;hou+=1;} if ((min>0)&&(flag==0)){window.alert("don't leave!!");flag=1;}document.forms["input1"]["value"]=hou+"时"+min+"分"+sec+"秒";idt=window.setTimeout("update();",1000);}</script></div></form>
</body>
</html>