Javascript 中的定时器: setTimeout() 和 setInterval()

定时器1：setTimeout()

<!DOCTYPE html>
<html>
  <head>
    <title>js12.html</title>
    <script type="text/javascript">
        function count()
        {
            setTimeout("alert('执行成功')",2000); //两秒钟后执行 alert
        }
    </script>
    
  </head>
  
  <body>
    <input type = "button" value = "计时开始" name = "timing" onclick="count()">
        
  </body>
</html>

第二种：setInterval()

<!DOCTYPE html>
<html>
  <head>
    <title>js13.html</title>
    
    <script type="text/javascript">
        var sec = 0;
        var timeId = setInterval("count();", 1000);//每隔 1 秒执行一次 count()
    
        function count()
        {
            document.getElementById("num").innerHTML = sec++;
        }
        function stop()
        {
            clearInterval(timeId);
        }
    </script>
  </head>
  
  <body>
    <font color="red" id ="num">0</font>秒钟
    <input type = "button" value = "停止" onclick="stop();" >
  </body>
</html>

结果：点击 Stop，计时停止