Fixed toFormData regression bug (unreleased) with Array-like object…

…s serialization; (#4714)

Added `toURLEncodedForm` helper;
Added automatic payload serialization to `application/x-www-form-urlencoded` to have parity with `multipart/form-data`;
Added test of handling `application/x-www-form-urlencoded` body by express.js;
Updated README.md;
Added missed param in JSDoc;
Fixed hrefs in README.md;

Co-authored-by: Jay <jasonsaayman@gmail.com>

README.md

@@ -39,12 +39,12 @@ Promise based HTTP client for the browser and node.js
     - [AbortController](#abortcontroller)
     - [CancelToken 👎](#canceltoken-deprecated)
   - [Using application/x-www-form-urlencoded format](#using-applicationx-www-form-urlencoded-format)
-    - [Browser](#browser)
-    - [Node.js](#nodejs)
-      - [Query string](#query-string)
-      - [Form data](#form-data)
-        - [Automatic serialization](#-automatic-serialization)
-        - [Manual FormData passing](#manual-formdata-passing)
+    - [URLSearchParams](#urlsearchparams)
+    - [Query string](#query-string-older-browsers)
+    - [🆕 Automatic serialization](#-automatic-serialization-to-urlsearchparams)        
+  - [Using multipart/form-data format](#using-multipartform-data-format)    
+    - [FormData](#formdata)
+    - [🆕 Automatic serialization](#-automatic-serialization-to-formdata) 
   - [Semver](#semver)
   - [Promises](#promises)
   - [TypeScript](#typescript)
@@ -61,6 +61,7 @@ Promise based HTTP client for the browser and node.js
 - Transform request and response data
 - Cancel requests
 - Automatic transforms for JSON data
+- 🆕 Automatic data object serialization to `multipart/form-data` and `x-www-form-urlencoded` body encodings
 - Client side support for protecting against [XSRF](https://en.wikipedia.org/wiki/Cross-site_request_forgery)
 
 ## Browser Support
@@ -814,7 +815,9 @@ cancel();
 
 > During the transition period, you can use both cancellation APIs, even for the same request:
 
-## Using application/x-www-form-urlencoded format
+## Using `application/x-www-form-urlencoded` format
+
+### URLSearchParams
 
 By default, axios serializes JavaScript objects to `JSON`. To send data in the [`application/x-www-form-urlencoded` format](https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/POST) instead, you can use the [`URLSearchParams`](https://developer.mozilla.org/en-US/docs/Web/API/URLSearchParams) API, which is [supported](http://www.caniuse.com/#feat=urlsearchparams) in the vast majority of browsers, [and Node](https://nodejs.org/api/url.html#url_class_urlsearchparams) starting with v10 (released in 2018).
 
@@ -824,7 +827,7 @@ params.append('extraparam', 'value');
 axios.post('/foo', params);
 ```
 
-### Older browsers
+### Query string (Older browsers)
 
 For compatibility with very old browsers, there is a [polyfill](https://github.com/WebReflection/url-search-params) available (make sure to polyfill the global environment).
 
@@ -863,9 +866,73 @@ You can also use the [`qs`](https://github.com/ljharb/qs) library.
 > NOTE: 
 > The `qs` library is preferable if you need to stringify nested objects, as the `querystring` method has [known issues](https://github.com/nodejs/node-v0.x-archive/issues/1665) with that use case.
 
-#### Form data
+### 🆕 Automatic serialization to URLSearchParams
+
+Axios will automatically serialize the data object to urlencoded format if the content-type header is set to "application/x-www-form-urlencoded".
+
+```
+const data = {
+  x: 1,
+  arr: [1, 2, 3],
+  arr2: [1, [2], 3],
+  users: [{name: 'Peter', surname: 'Griffin'}, {name: 'Thomas', surname: 'Anderson'}],
+};
+
+await axios.postForm('https://postman-echo.com/post', data,
+  {headers: {'content-type': 'application/x-www-form-urlencoded'}}
+);
+```
+
+The server will handle it as 
+
+```js
+  {
+    x: '1',
+    'arr[]': [ '1', '2', '3' ],
+    'arr2[0]': '1',
+    'arr2[1][0]': '2',
+    'arr2[2]': '3',
+    'arr3[]': [ '1', '2', '3' ],
+    'users[0][name]': 'Peter',
+    'users[0][surname]': 'griffin',
+    'users[1][name]': 'Thomas',
+    'users[1][surname]': 'Anderson'
+  }
+````
+
+If your backend body-parser (like `body-parser` of `express.js`) supports nested objects decoding, you will get the same object on the server-side automatically
+
+```js
+  var app = express();
+  
+  app.use(bodyParser.urlencoded({ extended: true })); // support encoded bodies
+  
+  app.post('/', function (req, res, next) {
+     // echo body as JSON
+     res.send(JSON.stringify(req.body));
+  });
+
+  server = app.listen(3000);
+```
+
+## Using `multipart/form-data` format
+
+### FormData
+
+In node.js, you can use the [`form-data`](https://github.com/form-data/form-data) library as follows:
+
+```js
+const FormData = require('form-data');
+ 
+const form = new FormData();
+form.append('my_field', 'my value');
+form.append('my_buffer', new Buffer(10));
+form.append('my_file', fs.createReadStream('/foo/bar.jpg'));
+
+axios.post('https://example.com', form)
+```
 
-##### 🆕 Automatic serialization
+### 🆕 Automatic serialization to FormData
 
 Starting from `v0.27.0`, Axios supports automatic object serialization to a FormData object if the request `Content-Type` 
 header is set to `multipart/form-data`.
@@ -904,7 +971,7 @@ Axios FormData serializer supports some special endings to perform the following
 - `[]` - unwrap the array-like object as separate fields with the same key 
 
 > NOTE: 
-> unwrap/expand operation will be used by default on array-like objects
+> unwrap/expand operation will be used by default on arrays and FileList objects
 
 FormData serializer supports additional options via `config.formSerializer: object` property to handle rare cases:
 
@@ -976,21 +1043,6 @@ await axios.postForm('https://httpbin.org/post', document.querySelector('#fileIn
 
 All files will be sent with the same field names: `files[]`;
 
-##### Manual FormData passing
-  
-In node.js, you can use the [`form-data`](https://github.com/form-data/form-data) library as follows:
-
-```js
-const FormData = require('form-data');
-
-const form = new FormData();
-form.append('my_field', 'my value');
-form.append('my_buffer', new Buffer(10));
-form.append('my_file', fs.createReadStream('/foo/bar.jpg'));
-
-axios.post('https://example.com', form)
-```
-
 ## Semver
 
 Until axios reaches a `1.0` release, breaking changes will be released with a new minor version. For example `0.5.1`, and `0.5.4` will have the same API, but `0.6.0` will have breaking changes.

lib/defaults/index.js

@@ -5,6 +5,7 @@ var normalizeHeaderName = require('../helpers/normalizeHeaderName');
 var AxiosError = require('../core/AxiosError');
 var transitionalDefaults = require('./transitional');
 var toFormData = require('../helpers/toFormData');
+var toURLEncodedForm = require('../helpers/toURLEncodedForm');
 
 var DEFAULT_CONTENT_TYPE = {
   'Content-Type': 'application/x-www-form-urlencoded'
@@ -71,18 +72,26 @@ var defaults = {
     }
 
     var isObjectPayload = utils.isObject(data);
-    var contentType = headers && headers['Content-Type'];
-
+    var contentType = headers && headers['Content-Type'] || '';
     var isFileList;
 
-    if ((isFileList = utils.isFileList(data)) || (isObjectPayload && contentType === 'multipart/form-data')) {
-      var _FormData = this.env && this.env.FormData;
-      return toFormData(
-        isFileList ? {'files[]': data} : data,
-        _FormData && new _FormData(),
-        this.formSerializer
-      );
-    } else if (isObjectPayload || contentType === 'application/json') {
+    if (isObjectPayload) {
+      if (contentType.indexOf('application/x-www-form-urlencoded') !== -1) {
+        return toURLEncodedForm(data).toString();
+      }
+
+      if ((isFileList = utils.isFileList(data)) || contentType.indexOf('multipart/form-data') !== -1) {
+        var _FormData = this.env && this.env.FormData;
+
+        return toFormData(
+          isFileList ? {'files[]': data} : data,
+          _FormData && new _FormData(),
+          this.formSerializer
+        );
+      }
+    }
+
+    if (isObjectPayload || contentType.indexOf('application/json') !== -1) {
       setContentTypeIfUnset(headers, 'application/json');
       return stringifySafely(data);
     }

lib/helpers/buildURL.js

@@ -17,6 +17,7 @@ function encode(val) {
  *
  * @param {string} url The base of the url (e.g., http://www.google.com)
  * @param {object} [params] The params to be appended
+ * @param {?object} paramsSerializer
  * @returns {string} The formatted url
  */
 module.exports = function buildURL(url, params, paramsSerializer) {

lib/helpers/toFormData.js

@@ -20,6 +20,20 @@ function renderKey(path, key, dots) {
   }).join(dots ? '.' : '');
 }
 
+function convertValue(value) {
+  if (value === null) return '';
+
+  if (utils.isDate(value)) {
+    return value.toISOString();
+  }
+
+  if (utils.isArrayBuffer(value) || utils.isTypedArray(value)) {
+    return typeof Blob === 'function' ? new Blob([value]) : Buffer.from(value);
+  }
+
+  return value;
+}
+
 function isFlatArray(arr) {
   return utils.isArray(arr) && !arr.some(isVisitable);
 }
@@ -64,21 +78,6 @@ function toFormData(obj, formData, options) {
     throw new TypeError('visitor must be a function');
   }
 
-  function convertValue(value) {
-    if (value === null) return '';
-
-    if (utils.isDate(value)) {
-      return value.toISOString();
-    }
-
-    if (utils.isArrayBuffer(value) || utils.isTypedArray(value)) {
-      return typeof Blob === 'function' ? new Blob([value]) : Buffer.from(value);
-    }
-
-    return value;
-  }
-
-
   /**
    *
    * @param {*} value
@@ -88,15 +87,18 @@ function toFormData(obj, formData, options) {
    * @returns {boolean} return true to visit the each prop of the value recursively
    */
   function defaultVisitor(value, key, path) {
-    var arr;
+    var arr = value;
 
     if (value && !path && typeof value === 'object') {
       if (utils.endsWith(key, '{}')) {
         // eslint-disable-next-line no-param-reassign
         key = metaTokens ? key : key.slice(0, -2);
         // eslint-disable-next-line no-param-reassign
         value = JSON.stringify(value);
-      } else if (!utils.isPlainObject(value) && (arr = utils.toArray(value)) && isFlatArray(arr)) {
+      } else if (
+        (utils.isArray(value) && isFlatArray(value)) ||
+        (utils.isFileList(value) || utils.endsWith(key, '[]') && (arr = utils.toArray(value))
+        )) {
         // eslint-disable-next-line no-param-reassign
         key = removeBrackets(key);
 
@@ -138,7 +140,7 @@ function toFormData(obj, formData, options) {
     stack.push(value);
 
     utils.forEach(value, function each(el, key) {
-      var result = !utils.isUndefined(el) && defaultVisitor.call(
+      var result = !utils.isUndefined(el) && visitor.call(
         formData, el, utils.isString(key) ? key.trim() : key, path, exposedHelpers
       );
 
@@ -150,8 +152,8 @@ function toFormData(obj, formData, options) {
     stack.pop();
   }
 
-  if (!utils.isPlainObject(obj)) {
-    throw new TypeError('data must be a plain object');
+  if (!utils.isObject(obj)) {
+    throw new TypeError('data must be an object');
   }
 
   build(obj);

lib/helpers/toURLEncodedForm.js

@@ -0,0 +1,18 @@
+'use strict';
+
+var utils = require('../utils');
+var toFormData = require('./toFormData');
+var platform = require('../platform/');
+
+module.exports = function toURLEncodedForm(data) {
+  return toFormData(data, new platform.classes.URLSearchParams(), {
+    visitor: function(value, key, path, helpers) {
+      if (platform.isNode && utils.isBuffer(value)) {
+        this.append(key, value.toString('base64'));
+        return false;
+      }
+
+      return helpers.defaultVisitor.apply(this, arguments);
+    }
+  });
+};

lib/platform/browser/classes/URLSearchParams.js

@@ -0,0 +1,38 @@
+'use strict';
+
+module.exports = (function getURLSearchParams(nativeURLSearchParams) {
+  if (typeof nativeURLSearchParams === 'function') return nativeURLSearchParams;
+
+  function encode(str) {
+    var charMap = {
+      '!': '%21',
+      "'": '%27',
+      '(': '%28',
+      ')': '%29',
+      '~': '%7E',
+      '%20': '+',
+      '%00': '\x00'
+    };
+    return encodeURIComponent(str).replace(/[!'\(\)~]|%20|%00/g, function replacer(match) {
+      return charMap[match];
+    });
+  }
+
+  function URLSearchParams() {
+    this.pairs = [];
+  }
+
+  var prototype = URLSearchParams.prototype;
+
+  prototype.append = function append(name, value) {
+    this.pairs.push([name, value]);
+  };
+
+  prototype.toString = function toString() {
+    return this.pairs.map(function each(pair) {
+      return pair[0] + '=' + encode(pair[1]);
+    }, '').join('&');
+  };
+
+  return URLSearchParams;
+})(URLSearchParams);

lib/platform/browser/index.js

@@ -0,0 +1,8 @@
+'use strict';
+
+module.exports = {
+  isBrowser: true,
+  classes: {
+    URLSearchParams: require('./classes/URLSearchParams')
+  }
+};

lib/platform/index.js

@@ -0,0 +1,3 @@
+'use strict';
+
+module.exports = require('./node/');

lib/platform/node/classes/URLSearchParams.js

@@ -0,0 +1,5 @@
+'use strict';
+
+var url = require('url');
+
+module.exports = url.URLSearchParams;

lib/platform/node/index.js

@@ -0,0 +1,8 @@
+'use strict';
+
+module.exports = {
+  isNode: true,
+  classes: {
+    URLSearchParams: require('./classes/URLSearchParams')
+  }
+};