title: append files to FormData not work in angularjs
body: <p>I use angularjs to upload files and json object to nodejs server in single request. Then I get this console.log on firebug:</p>
  
  <pre><code>-----------------------------8791641017658 Content-Disposition: form-data; name="model" {"phone":"asasasa","description":"121212112","payment":"2121212121","shipping":"121221221","imageurl":"21212112","price":"212112212","status":"new"} -----------------------------8791641017658--
  </code></pre>
  
  <p>So, the name="file" does not appear here. </p>
  
  <p>And the console.log(req.files) in nodejs server <code>// print out "{}"</code></p>
  
  <p>Please help, thank!</p>
  
  <pre><code>$scope.files = [];
  
          $scope.$on("fileSelected", function (event, args) {
  
          $scope.$apply(function () {            
              //add the file object to the scope's files collection
              $scope.files.push(args.file);
              console.log($scope.files);
  
          });
          });
  
      $scope.create = function() {
          $scope.seller_submit = {
              phone: this.phone,
              description: this.description,
              payment: this.payment,
              shipping: this.shipping,
              imageurl: this.imageurl,
              price: this.price,
              status: this.status
          };
  
          $http({
              method: 'POST',
              url: '/articles/'+ $routeParams.articleId,
  
              headers: { 'Content-Type': undefined },
  
              transformRequest: function (data) {
                  var formData = new FormData();
  
                  formData.append("model", angular.toJson(data.model));
  
                  for (var i = 0; i &lt; data.files; i++) {
  
                      formData.append("file" + i, data.files[i]);
                  }
                  return formData;
              },
  
              data: { model: $scope.seller_submit, files: $scope.files }
  
          }).
          success(function (data, status, headers, config) {
              alert("success!");
          }).
          error(function (data, status, headers, config) {
              alert("failed!");
          });
  </code></pre>