js插件简单拖拽

　　前端开发的时候，有好多地方用到拖拽效果,当然 http://jqueryui.com/draggable/ 是个不错的选择,but 我是个打破砂锅问到底的人，抽点时间用js小小的实现了类似的插件，话不多说。

　first:　html和css

<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <title></title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }

        #div1 {
            position: absolute;
            width: 100px;
            height: 100px;
            cursor: move;
            background-color: red;
        }
    </style>
</head>
<body>
    <div id="div1">
    </div>
</body>
</html>

now,先把主要算法实现一下：

 <script>
        window.onload = function () {
            //获取需要拖拽的div
            var div1 = document.getElementById("div1");
            //添加鼠标按下事件
            div1.onmousedown = function (evt) {
                var oEvent = evt || event;
                //获取按下鼠标到div left  top的距离
                var distanceX = oEvent.clientX - div1.offsetLeft;
                var distanceY = oEvent.clientX - div1.offsetTop;
                //添加doc滑动时间
                document.onmousemove = function (evt) {
                    var oEvent = evt || event;
                    //重新计算div的left top值
                    var left = oEvent.clientX - distanceX;
                    var top = oEvent.clientY - distanceY;

                    //left  当小于等于零时，设置为零 防止div拖出document之外
                    if (left <= 0) {
                        left = 0;
                    }
                    //当left 超过文档右边界  设置为右边界
                    else if (left >= document.documentElement.clientWidth - div1.offsetWidth) {
                        left = document.documentElement.clientWidth - div1.offsetWidth;
                    }
                    if (top <= 0) {
                        top = 0;
                    }
                    else if (top >= document.documentElement.clientHeight - div1.offsetHeight) {
                        top = document.documentElement.clientHeight - div1.offsetHeight;
                    }

                    //重新给div赋值
                    div1.style.top = top + "px";
                    div1.style.left = left + "px";
                }
                //添加鼠标抬起事件
                div1.onmouseup = function () {
                    //清空事件
                    document.onmousemove = null;
                    div1.onmouseup = null;
                }
            }
        }

    </script>

yeah,使用面向对象实现一下

<style>
        * {
            margin:0;
            padding:0;
        }
        #div1 {
            width: 100px;
            height: 100px;
            background-color: red;
        }
        #div2 {
            background-color:yellow;
            width:100px;
            height:100px;
        }
    </style>

<div id="div1"></div>
<div id="div2"></div>

js Draggle class:

 function Drag(id) {
            this.div = document.getElementById(id);
            if (this.div) {
                this.div.style.cursor = "move";
                this.div.style.position = "absolute";
            }

            this.disX = 0;
            this.disY = 0;
            var _this = this;

            this.div.onmousedown = function (evt) {
                _this.getDistance(evt);

                document.onmousemove = function (evt) {
                    _this.setPosition(evt);
                }

                _this.div.onmouseup = function () {
                    _this.clearEvent();
                }
            }
        }

        Drag.prototype.getDistance = function (evt) {
            var oEvent = evt || event;
            this.disX = oEvent.clientX - this.div.offsetLeft;
            this.disY = oEvent.clientY - this.div.offsetTop;
        }

        Drag.prototype.setPosition = function (evt) {
            var oEvent = evt || event;
            var l = oEvent.clientX - this.disX;
            var t = oEvent.clientY - this.disY;
            if (l <= 0) {
                l = 0;
            }
            else if (l >= document.documentElement.clientWidth - this.div.offsetWidth) {
                l = document.documentElement.clientWidth - this.div.offsetWidth;
            }
            if (t <= 0) {
                t = 0;
            }
            else if (t >= document.documentElement.clientHeight - this.div.offsetHeight) {
                t = document.documentElement.clientHeight - this.div.offsetHeight;
            }
            this.div.style.left = l + "px";
            this.div.style.top = t + "px";
        }

        Drag.prototype.clearEvent = function () {
            this.div.onmouseup = null;
            document.onmousemove = null;
        }

at last：最终实现：

  window.onload = function () {
            new Drag("div1");
            new Drag("div2");
        }

效果如下:

　　入园子已经三载有余，平时也爱在各位经营的园子溜达汲取知识。之前也有过想开一个自己的园子，但总因为这样那样的事情把这事遗忘了。最近发现身边的@考拉熊http://home.cnblogs.com/u/rccc/好早已经有了这个习惯。人啊，怎么说呢，总是向比自己强的人看起！加油，u can @o(∩_∩)o 哈哈

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原文地址：https://www.cnblogs.com/CharlieLau/p/4335721.html