js获取前端在本地上传图片的尺寸方法

var MyTest = document.getElementById("upload_img").
files[0];var reader = new FileReader();
reader.readAsDataURL(MyTest);
reader.onload = function(theFile)
 {　
 　var image = new Image(); 
 　 image.src = theFile.target.result; 
 　 image.onload = function() 
 　 { 
 　 　 alert("图片的宽度为"+this.width+",长度为"+this.height); };
};

<input type="file" size="20" autocomplete="off" id="upload_img" name="Uploadfile">