cocos2d js 怎样动态载入外部图片

官网没有详细样例，仅仅有看api，研究成果例如以下

        var that = this;
        var url = "http://xxxxxx";
        cc.loader.loadImg(url, null, function(err,img){
        	var logo  = new cc.Sprite(img);
        	that.addChild(logo);
        	logo.x = size.width / 2;
        	logo.y = size.height / 2;
        });