多次向左移动后，走到了浏览器外边怎么办？
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<script src="http://libs.baidu.com/jquery/1.9.0/jquery.js" type="text/javascript"></script>
<title>jQuery动画特效</title>
<style type="text/css">
div{
width: 30px;
height: 30px;
border: 1px solid #999;
border-radius: 50%;
background-color: orange;
position: absolute;
left: 100px;
}
input{
margin-top: 60px;
margin-left: 40px;
}
</style>
</head>
<body>
<div></div>
<input type="button" value="左移" id="left">
<input type="button" value="右移" id="right">
<span></span>
<script type="text/javascript">
$(function(){
$("#left").bind('click',function(){
$("div").animate({
left:'-=50px'
},3000,function(){
$("span").html("左移50像素");
});
});
$("#right").bind('click',function(){
$("div").animate({
left:'+=100px'
},3000,function(){
$("span").html("右移100像素");
});
});
})
</script>
</body>
</html>
