http://www.cnblogs.com/fsjohnhuang/p/3925827.html

https://github.com/fsjohnhuang/preview/releases/tag/v1.2.0

    if (isRender(_, _.fileEl.files[0].name, isExpectedMIME)){ if (!img){
         img = new Image();  img.className = imgCls; 

 // img.style.width = previewEl.offsetWidth + 'px'; 

 // img.style.height = previewEl.offsetHeight + 'px';  

// previewEl.appendChild(img);  

}
      img.src = src;  img.style.width = "200px";   

alert("2图片的宽度为"+img.width+",2长度为"+img.height); 

//    img.style.height = img.offsetHeight;  

img.onload = function(){ 

alert("图片的宽度为"+this.width+",长度为"+this.height);  

previewEl.appendChild(img);  

var imgwidth = img.width;  

var imgheight = img.height;  

alert(imgwidth + "," + imgheight);  

};      

}