javascript实现拖放，地图推移，

startDrag: function(elem) {
elem.onmousedown =function(ev) {
dragObject  = this;
mouseOffset = ws.m.pin.getMouseOffset(this, ev);
return false;
}

},

//information on where we clicked our item
getMouseOffset:function (target, ev){
ev = ev || window.event; 
var mousePos  = ws.m.pin.mouseCoords(ev);
var docPos    = ws.m.pin.getPosition(target);
return {x:mousePos.x - docPos.x, y:mousePos.y - docPos.y};
},

//the coordinates of an item relative to the document
getPosition:function (e){

var left = 0;
var top  = 0;
left = e.offsetLeft ;
top  = e.offsetTop ;
return {x:left, y:top};
},

//capture the mouse coordinates
mouseCoords:function (ev){
if(ev.pageX || ev.pageY){
    return {x:ev.pageX, y:ev.pageY};
}
return {
    x:ev.clientX + document.body.scrollLeft - document.body.clientLeft,
    y:ev.clientY + document.body.scrollTop  - document.body.clientTop
};
        },

//Moving an Item
mouseMove:function  (ev)  {
ev  =  ev  ||  window.event;