鼠标拖拽

鼠标拖拽
<!DOCTYPE html>
<html lang="zh">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        #box {
            width: 2cm;
            height: 200px;
            background-color: red;
            /* 绝对位置 */
            position: absolute;
        }
    </style>
</head>

<body>
    <div id="box"></div>
    <script>
        let box = document.getElementById("box")
        box.onmousedown = function (e) {
            let ox = e.offsetX
            let oy = e.offsetY
            document.onmousemove = function (e2) {
                let cx = e2.clientX
                let cy = e2.clientY
                let _left = cx - ox
                let _top = cy - oy
                if (_left < 0) {
                    _left = 0
                }
                if (_top < 0) {
                    _top = 0
                }
                if (_left > document.documentElement.clientWidth - box.offsetWidth) {
                    _left = document.documentElement.clientWidth - box.offsetWidth
                }
                if (_top > document.documentElement.clientHeight - box.offsetHeight) {
                    _top = document.documentElement.clientHeight - box.offsetHeight
                }
                box.style.left = _left + "px"
                box.style.top = _top + "px"

            }
        }
        document.onmouseup = function () {
            document.onmousemove = null
        }
    </script>
</body>

</html>
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