<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
</head>
<body>
<div style="border :1px solid red; width :500px;height :300px ; overflow:hidden; margin:20px">
<div id="blackSquare" style="position: relative; 50px; height:50px; background-color: black;cursor: pointer;color:#fff">wjw</div>
</div>
</body>
<script>
window.onload = () => {
//获取拖拽实验对象
let el=document.getElementById("blackSquare");
//在该对象上绑定鼠标点击事件
el.onmousedown = (e) => {
//鼠标按下，计算鼠标触点距离元素左侧的距离
let disX = e.clientX - el.offsetLeft;
let disY = e.clientY - el.offsetTop;
document.onmousemove = function (e) {
//计算需要移动的距离
let t = e.clientX - disX;
let P = e.clientY - disY;
//移动当前元素
if (t >= 0 && t <= window.innerWidth - el.offsetWidth) {
el.style.left = t + 'px';
}
//移动当前元素
if (P >= 0 && P <= window.innerHeight - el.offsetHeight ) {
el.style.top = P + 'px';
}
};
//鼠标松开时，注销鼠标事件，停止元素拖拽。
document.onmouseup = function (e) {
document.onmousemove = null;
document.onmouseup = null;
};
}
}
</script>
</html>
