为什么我得出图片的长宽都为null?

loadPicSize:function(sourceSrc){
			console.log(sourceSrc);
			var self =this;

			this.preLoadImg(sourceSrc,function(){

				self.popupPic.attr("src",sourceSrc);
				console.log("self.popupPic:"+self.popupPic);
				var picWidth =self.popupPic.width();
				var picHeight=self.popupPic.height();
				console.log("picWidth:"+picWidth);
				console.log("picHeight:"+picHeight);
			});
		},
		preLoadImg:function(src,callback){
			 var img=new Image();
            if(!!window.ActiveXObject){
                img.onreadystatechange=function(){
                    if (this.readyState=="complete") {
                        callback();
                    };
                };
            }else {
                img.onload=function(){
                    callback();
                };
            };
            img.src=src;
		},

代码如上，报错如下

这个问题卡了好久求解答！