试试这样的吧
<body>
<div id="box" style="height:2000px;width:3000px;">
<div id="div1" style="width:500px;height:500px;background:green;position:absolute;">
<div id="div2" style="width:200px;height:100px;background:lightblue;position:fixed;">里面的div</div>
</div>
</div>
</body>
<script type="text/javascript">
var sTop = 0; //初始卷起的高度
var sLeft = 0; //初始卷起的宽度
var p_div = document.getElementById("div1"); //父div
var max_x = p_div.offsetLeft+p_div.offsetWidth; //父div的右边界
var max_y = p_div.offsetTop+p_div.offsetHeight; //父div的下边界
window.onscroll = function(){
var c_div = document.getElementById("div2"); //子div
var s_top = document.documentElement.scrollTop || document.body.scrollTop; //卷起的高度
var s_left = document.documentElement.scrollLeft || document.body.scrollLeft; //卷起的宽度
if(s_top!=sTop){ //纵向滚动,当前卷起的高度和原卷起的高度不一致
sTop = s_top;
c_y = s_top+p_div.offsetTop+c_div.offsetHeight; //子div当前的下边界坐标
if(c_y>=max_y){ //如果下边界超过父div下边界
c_div.style.position = "relative";
c_div.style.top = (p_div.offsetHeight-c_div.offsetHeight)+"px";
c_div.style.left = s_left+"px";
}else{
c_div.style.position = "fixed";
c_div.style.top = "";
c_div.style.left = "";
}
}
if(s_left!=sLeft){ //纵向滚动
sLeft = s_left;
c_x = s_left+p_div.offsetLeft+c_div.offsetWidth;
if(c_x>=max_x){
c_div.style.position = "relative";
c_div.style.left = (p_div.offsetWidth-c_div.offsetWidth)+"px";
c_div.style.top = s_top+"px";
}else{
c_div.style.position = "fixed";
c_div.style.left = "";
c_div.style.top = "";
}
}
}
</script>
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