效果：
代码实现：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
<style>
.box1{
width: 50px;
height: 50px;
background: red;
position: absolute;
z-index: 999;
}
.box2{
width: 50px;
height: 50px;
background: yellow;
position: absolute;
left: 500px;
top: 500px;
}
</style>
<div class="box1"></div>
<div class="box2"></div>
<script>
let box1 = document.querySelector(".box1")
box1.addEventListener("mousedown",function(event){
// div的相对于鼠标的偏移量
let x = event.clientX - box1.offsetLeft;
let y = event.clientY - box1.offsetTop;
// 给document增加鼠标移动事件
document.onmousemove = function(event){
event = event || window.event
let left = event.clientX - x;
let top = event.clientY - y;
// 元素的位置更新
box1.style.left = left + px;
box1.style.top = top + px
}
document.onmouseup = function(){
// 移除document的鼠标移动事件以及鼠标弹开事件
document.onmousemove = null;
document.onmouseup = null;
}
})
</script>
</body>
</html>
