(function($){$.fn.extend({mydrag:function(){var boxX = 0;        //元素在页面中的横坐标var boxY = 0;        //元素在页面中的纵坐标var dMouseX = 0;    //按下鼠标时的鼠标所在位置的横坐标var dMouseY = 0;    //按下鼠标时的鼠标所在位置的纵坐标var mMouseX = 0;    //移动鼠标时的鼠标所在位置的横坐标var mMouseY = 0;    //移动鼠标时的鼠标所在位置的纵坐标var moveLenX = 0;    //存放鼠标移动的距离，横向var moveLenY = 0;    //存放鼠标移动的距离，纵向var isMove = false;    //是否拖动层的一个输助"开关"var movingX = 0;    //移动中元素的LEFT值var movingY = 0;    //移动中元素的TOP值//可视区域最右边的值var rightest = document.documentElement.clientWidth - $(".top").parent().outerWidth();//可视区域最右边的值var bottomest = document.documentElement.clientHeight - $(".top").parent().outerHeight();//获得移动鼠标时的鼠标所在位置的坐标var getMoveMouse = function(move){mMouseX = move.pageX;mMouseY = move.pageY;}//获得元素在页面中的当前的位置var getbox = function(m){boxX = $(".box").offset().left;boxY = $(".box").offset().top;}//获得鼠标按下时的坐标var getDownMouse = function(m){dMouseX = m.pageX;dMouseY = m.pageY;}//获得鼠标移动的距离值var getMoveLen = function(){moveLenX = mMouseX - dMouseX;moveLenY = mMouseY - dMouseY;}//鼠标UP时，关闭移动，即鼠标移动也不会让元素移动；$(document).mouseup(function(){isMove = false;})//给元素的TOP绑定事件$(this).//按下时获得元素的坐标和当前鼠标的坐档；mousedown(function(e){getbox(e);getDownMouse(e)isMove = true;}).//移动时获得移动的距离，设置元素的TOP和LEFT值；mousemove(function(e){var $this = $(this);getMoveMouse(e);getMoveLen();if(isMove){//防止元素移出可视区域//可视区域浏览器最左边if(movingX<0){$this.css({"left":0});if(movingY<0){$this.css({"top":0});}else if(movingY > bottomest){$this.css({"top":bottomest});}else{$this.css({"top":boxY+moveLenY});}}//可视区域浏览器最上面else if(movingY<0){$this.css({"top":0});if(movingX>rightest){$this.css({"left":rightest});    }else{$this.css({"left":boxX+moveLenX});    }}//可视区域浏览器最右边else if(movingX > rightest){$this.css({"left":rightest});if(movingY > bottomest){$this.css({"top":bottomest});    }else{$this.css({"top":boxY+moveLenY});}}//可视区域浏览器最下边else if(movingY > bottomest){$this.css({"top":bottomest});    if(movingX<0){$this.css({"left":0});    }else{$this.css({"left":boxX+moveLenX});    }    }//其它情况，即在可视区域中间else{$this.css({"left":boxX+moveLenX,"top":boxY+moveLenY});    }movingX = boxX+moveLenX;movingY = boxY+moveLenY;}})    }    })
})(jQuery)