JavaScript: 让拖动支持iphone/ipad触摸

var getDragClass=(function(){

var SupportsTouches = ("createTouch" in document),//判断是否支持触摸

    StartEvent = SupportsTouches ? "touchstart" : "mousedown",//支持触摸式使用相应的事件替代

    MoveEvent = SupportsTouches ? "touchmove" : "mousemove",

    EndEvent = SupportsTouches ? "touchend" : "mouseup",

    $=function(id){

        return document.getElementById(id);

    },

    preventDefault=function(ev){

        if(ev)ev.preventDefault();

        else window.event.returnValue = false;

    },

    getMousePoint=function(ev){

        var x = y = 0,

            doc = document.documentElement,

            body = document.body;

            if(!ev) ev=window.event;

            if (window.pageYoffset) {

                x = window.pageXOffset;

                y = window.pageYOffset;

            }else{

                x = (doc && doc.scrollLeft || body && body.scrollLeft || 0) - (doc && doc.clientLeft || body && body.clientLeft || 0);

                y = (doc && doc.scrollTop  || body && body.scrollTop  || 0) - (doc && doc.clientTop  || body && body.clientTop  || 0);

            }

            if(SupportsTouches){

                var evt = ev.touches.item(0);//仅支持单点触摸,第一个触摸点

                x=evt.pageX;

                y=evt.pageY;

            }else{

                x += ev.clientX;

                y += ev.clientY;

            }

            return {'x' : x, 'y' : y};

    };

    function _drag(opt){

        this.el=typeof opt.el=='string'?$(opt.el):opt.el;//被拖动节点

        this.onstart=opt.start || new Function();//

        this.onmove=opt.move || new Function();

        this.onend=opt.end || new Function();

        this.action=false;

        this.init();

    }

    _drag.prototype={

        init:function(){

            this.el.style.position='relative';

            this.el['on'+StartEvent]=this.bind(function(e){//绑定节点的 [鼠标按下/触摸开始] 事件

                preventDefault(e);

                if(this.action)return false;

                else this.action=true;

                this.startPoint=getMousePoint(e);

                this.onstart();

                document['on'+MoveEvent]=this.bind(function(e){

                    preventDefault(e);//取消文档的默认行为[鼠标移动、触摸移动]

                    this.nowPoint=getMousePoint(e);

                    this.el.style.left=this.nowPoint.x-this.startPoint.x+'px';

                    this.el.style.top=this.nowPoint.y-this.startPoint.y+'px';

                    this.onmove();

                },this);

                document['on'+EndEvent]=document['ontouchcancel']=this.bind(function(){

                    document['on'+EndEvent]=document['ontouchcancel']=document['on'+MoveEvent]=null;

                    this.action=false;

                    this.onend();

                },this);

            },this);

        },

        bind:function(fn,obj){

            return function(){

                fn.apply(obj,arguments);

            }

        }

    }

    return function(opt){

        return new _drag(opt);

    }

})();