html代码
<div id="box"></div>
css代码
* {
margin: 0;
padding: 0;
}
#box {
width: 100px;
height: 100px;
background: red;
position: absolute;
}
JS代码
var Box = document.getElementById("box");
var iw = document.documentElement.clientWidth - Box.offsetWidth;
Box.onmousedown = function (e) {
var e = e || event;
var disX = e.offsetX;
var disY = e.offsetY;
document.onmousemove = function (e) {
var e = e || event;
var l = e.clientX - disX;
var t = e.clientY - disY;
l = l >= iw ? l = iw : (l <= 0 ? l = 0 : l = l);
t = t >= e.clientY ? t = e.clientY : (t <= 0 ? t = 0 : t = t);
Box.style.left = l + "px";
Box.style.top = t + "px";
};
document.onmouseup = function () {
document.onmousemove = null;
document.onmouseup = null;
}
}