console 命令行工具 X clear

console

function timedMsg()
{
var t=setTimeout("alert('5 seconds!')",5000)
}

<form> 
  <input type="button" value="显示计时的消息框！" onclick="timedMsg()"> 
 </form> 
 <p>点击上面的按钮。5 秒后会显示一个消息框。</p>