<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<style>
#box {
width: 50px;
height: 50px;
border: 10px solid #666;
position: fixed;
border-radius: 50%;
}
</style>
</head>
<body>
<div id='box'></div>
<script>
var box = document.getElementById('box')
box.onmousedown = function(ev) {
var disX = ev.clientX - box.offsetLeft
var disY = ev.clientY - box.offsetTop
document.onmousemove = function(ev) {
var left = ev.clientX - disX
var top = ev.clientY - disY
if (left < 0) {
left = 0
}
if (top < 0) {
top = 0
}
box.style.left = left + 'px'
box.style.top = top + 'px'
}
document.onmouseup = function() {
document.onmousemove = null;
document.onmouseup = null
}
}
<script>
</body>
</html>
要点1:css 必须设置position
要点2:鼠标事件的应用
要点3:鼠标弹起,事件清空
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