js获取上传图片大小

//转载:http://purplebamboo.github.io/2014/02/09/javascript-watch-img-width-height/
var input = document.getElementById("file");
if(input.files){
                //读取图片数据
  var f = input.files[0];
  var reader = new FileReader();
  reader.onload = function (e) {
      var data = e.target.result;
      //加载图片获取图片真实宽度和高度
      var image = new Image();
      image.onload=function(){
          var width = image.width;
          var height = image.height;
          alert(width+'======'+height+"====="+f.size);
      };
      image.src= data;
  };
  reader.readAsDataURL(f);
  }else{
  var image = new Image(); 
  image.onload =function(){
      var width = image.width;
      var height = image.height;
      var fileSize = image.fileSize;
      alert(width+'======'+height+"====="+fileSize);
  }
  image.src = input.value;

  }