onmousedown onmousemove onmouseup
<!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>
<style>
#box {
width: 100px;
height: 100px;
background: red;
position: absolute;
}
</style>
</head>
<body style="position: relative; overflow: hidden">
<div id="box"></div>
<script>
window.onload = function () {
let box = document.getElementById('box');
box.onmousedown = function (ev) {
let e = ev || event;
let x = e.clientX - box.offsetLeft; //鼠标点击坐标距离盒子左边缘的距离
let y = e.clientY - box.offsetTop; //鼠标点击坐标距离盒子上边缘的距离
document.onmousemove = function (ev) {
let e = ev || event;
box.style.left = ev.clientX - x + 'px';
box.style.top = ev.clientY - y + 'px';
let bodyScreenX = ev.screenX;
let bodyClientWidth = document.body.clientWidth;
document.onmouseup = function (ev) {
if (ev.clientX - x < 0) {
box.style.left = 0;
} else if (bodyScreenX > bodyClientWidth) {
box.style.right = 0;
box.style.left = bodyClientWidth - 100 + 'px';
}
document.onmousemove = null;
document.onmouseup = null;
};
};
};
};
</script>
</body>
</html>
