怎么判断flag是true还是false

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>回到顶部效果</title>
<style>
*{
margin:0;padding:0;
}
.box{
width:1190px;
margin:0 auto;
}
.box img{

}
#btn{
width:40px;height:40px;position:fixed;
left:50%;
bottom:30px;background:url(images/top_bg.png) no-repeat left top;
margin-left:610px;
}
#btn:hover{
background:url(images/top_bg.png) no-repeat left -40px;
width:40px;height:40px;
}
</style>
</head>
<body>
<script type="text/javascript">
window.onload=function(){
var btn=document.getElementById("btn");
var timer=null;
var flag=true;
window.onscroll=function(){
if(!flag){
clearInterval(timer);
}
flag=false;
};
btn.onclick=function(){

timer=setInterval(function(){
var top=document.documentElement.scrollTop||document.body.scrollTop;
var iSpeed=Math.floor(-top/8);
document.documentElement.scrollTop=document.body.scrollTop=top+iSpeed;
console.log(top+iSpeed);
flag=true;
if(top==0){
clearInterval(timer);
}
},30);

}
}

</script>

<div class="box">
<img src="images/tb_bg.jpg">
</div>
<a href="javascript:;" id="btn"></a>
</body>
</html>

天翼翱翔

浏览 4308回答 3

3回答

慕的地8582982

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

落叶1111

只是传了个参数，来增加一个判断条件

ruibin

你看程序的执行顺序就行。当执行这里时 window.onscroll=function(){ if(!flag){ clearInterval(timer); } flag=false; //此处吧flag设置为false； };document.documentElement.scrollTop=document.body.scrollTop=top+iSpeed; console.log(top+iSpeed); flag=true;//此处把flag设置为true if(top==0){ clearInterval(timer); }

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