Adding body serializer config method

README.md

@@ -330,6 +330,15 @@ These are the available config options for making requests. Only the `url` is re
     return Qs.stringify(params, {arrayFormat: 'brackets'})
   },
 
+  // `bodySerializer` is an optional function in charge of serializing `body`
+  bodySerializer: function (params) {
+      var formData = new FormData();
+      Object.entries(data).forEach(([key, value]) => {
+          formData.append(key, value);
+      });
+      return formData;
+  },
+
   // `data` is the data to be sent as the request body
   // Only applicable for request methods 'PUT', 'POST', 'DELETE , and 'PATCH'
   // When no `transformRequest` is set, must be of one of the following types:

examples/upload/index.html

@@ -22,14 +22,22 @@ <h1>file upload</h1>
       (function () {
         var output = document.getElementById('output');
         document.getElementById('upload').onclick = function () {
-          var data = new FormData();
-          data.append('foo', 'bar');
-          data.append('file', document.getElementById('file').files[0]);
+          var data = {
+            foo: 'bar',
+            file: document.getElementById('file').files[0],
+          };
 
           var config = {
             onUploadProgress: function(progressEvent) {
               var percentCompleted = Math.round( (progressEvent.loaded * 100) / progressEvent.total );
-            }
+            },
+            serializedBody: function(data) {
+              var formData = new FormData();
+              Object.entries(data).forEach(([key, value]) => {
+                formData.append(key, value);
+              });
+              return formData;
+            },
           };
 
           axios.put('/upload/server', data, config)

index.d.ts

@@ -56,6 +56,7 @@ export interface AxiosRequestConfig {
   headers?: any;
   params?: any;
   paramsSerializer?: (params: any) => string;
+  bodySerializer?: (body: any) => any;
   data?: any;
   timeout?: number;
   timeoutErrorMessage?: string;

lib/core/Axios.js

@@ -47,6 +47,10 @@ Axios.prototype.request = function request(config) {
     config.method = 'get';
   }
 
+  if (config.bodySerializer) {
+    config.data = config.bodySerializer(config.data);
+  }
+
   var transitional = config.transitional;
 
   if (transitional !== undefined) {

lib/core/mergeConfig.js

@@ -18,7 +18,7 @@ module.exports = function mergeConfig(config1, config2) {
   var valueFromConfig2Keys = ['url', 'method', 'data'];
   var mergeDeepPropertiesKeys = ['headers', 'auth', 'proxy', 'params'];
   var defaultToConfig2Keys = [
-    'baseURL', 'transformRequest', 'transformResponse', 'paramsSerializer',
+    'baseURL', 'transformRequest', 'transformResponse', 'paramsSerializer', 'bodySerializer',
     'timeout', 'timeoutMessage', 'withCredentials', 'adapter', 'responseType', 'xsrfCookieName',
     'xsrfHeaderName', 'onUploadProgress', 'onDownloadProgress', 'decompress',
     'maxContentLength', 'maxBodyLength', 'maxRedirects', 'transport', 'httpAgent',