Angularjs实现上传图片预览功能

<input type="file" ng-file-select="onfileselect($files)" accept="image/*">
app.factory("filereader", function($q, $log) {
      var onload = function(reader, deferred, scope) {
        return function () {
          scope.$apply(function () {
            deferred.resolve(reader.result);
          });
        };
      };
      var onerror = function (reader, deferred, scope) {
        return function () {
          scope.$apply(function () {
            deferred.reject(reader.result);
          });
        };
      };
      var onprogress = function(reader, scope) {
        return function (event) {
          scope.$broadcast("fileprogress",
              {
                total: event.total,
                loaded: event.loaded
              });
        };
      };
      var getreader = function(deferred, scope) {
        var reader = new filereader();
        reader.onload = onload(reader, deferred, scope);
        reader.onerror = onerror(reader, deferred, scope);
        reader.onprogress = onprogress(reader, scope);
        return reader;
      };
      var readasdataurl = function (file, scope) {
        var deferred = $q.defer();
        var reader = getreader(deferred, scope);
        reader.readasdataurl(file);
        return deferred.promise;
      };
      return {
        readasdataurl: readasdataurl
      };
  });

$scope.onfileselect = function(files) {
      var filein=files[0];
      var img = new image();
      var filetype = filein.name.substring(filein.name.lastindexof(".") + 1, filein.name.length);
      if(filein.size>5242880){//单位是b，此处不允许超过5m
        alert("图片不能超过5m")
        return;
      }
      if(filetype=='jpg' || filetype=='png' || filetype=='jpeg ' || filetype=='jpg' || filetype=='png' || filetype=='jpeg'){
      }else{
        alert("图片格式只支持:jpg,png,jpeg")
        return;
      }
      filereader.readasdataurl(filein, $scope)
          .then(function(result) {
            $scope.imagesrc = result;
            console.log(img.width);
      });
    }