前端：javascript定时器

<script type="text/javascript">
    $(document).ready(function(){ 
        alert("开启定时器"); 
        //setTimerOut只执行一次
        //window.id=window.setTimeout(hello,5000);
            
        //setInterval反复执行
        window.id=window.setInterval(hello,5000);
            
    });  
        
    function hello(){ 
           alert("hello"); 
    } 
        
    function clearTimer(id){
        // window.clearTimeout(id); 
        window.clearInterval(id); 
    }
</script>