Improved FormData support; (#4448)

* Fixed isFormData predicate;
Added support for automatic object serialization to FormData if `Content-Type` is `multipart/form-data`;
Added support for FormData to be overloaded using `config.env.FormData` option;
Added support for FormData in node.js environment through `form-data` package;

* Added the `form-data` package as a dependency for the server build;
Added tests for FormData payload;

* Added FormData automatic serialization section;
Refactored cancellation section;

* Reworked toFormData helper;
Expose toFormData helper as a static method;
Refactored transform request;
Added kindOf, kindOfTest, endsWith, isTypedArray util;
Refactored utils.js to use kindOf for tests;

* Fixed isFormData predicate; (#4413)

Added support for automatic object serialization to FormData if `Content-Type` is `multipart/form-data`;
Added support for FormData to be overloaded using `config.env.FormData` option;
Added support for FormData in node.js environment using `form-data` package;

(cherry picked from commit 73e3bdb883)

* Added shortcut methods `postForm`, `putForm`, `patchForm` to submit a Form;
Added ability to submit FileList object as a FormData;
Updated README.md;

* Updated README.md;

lib/helpers/toFormData.js

@@ -1,55 +1,73 @@
 'use strict';
 
-function combinedKey(parentKey, elKey) {
-  return parentKey + '.' + elKey;
-}
-
-function buildFormData(formData, data, parentKey) {
-  if (Array.isArray(data)) {
-    data.forEach(function buildArray(el, i) {
-      buildFormData(formData, el, combinedKey(parentKey, i));
-    });
-  } else if (
-    typeof data === 'object' &&
-    !(data instanceof File || data === null)
-  ) {
-    Object.keys(data).forEach(function buildObject(key) {
-      buildFormData(
-        formData,
-        data[key],
-        parentKey ? combinedKey(parentKey, key) : key
-      );
-    });
-  } else {
-    if (data === undefined) {
-      return;
-    }
-
-    var value =
-      typeof data === 'boolean' || typeof data === 'number'
-        ? data.toString()
-        : data;
-    formData.append(parentKey, value);
-  }
-}
+var utils = require('../utils');
 
 /**
- * convert a data object to FormData
- *
- * type FormDataPrimitive = string | Blob | number | boolean
- * interface FormDataNest {
- *   [x: string]: FormVal
- * }
- *
- * type FormVal = FormDataNest | FormDataPrimitive
- *
- * @param {FormVal} data
- */
+ * Convert a data object to FormData
+ * @param {Object} obj
+ * @param {?Object} [formData]
+ * @returns {Object}
+ **/
 
-module.exports = function getFormData(data) {
-  var formData = new FormData();
+function toFormData(obj, formData) {
+  // eslint-disable-next-line no-param-reassign
+  formData = formData || new FormData();
 
-  buildFormData(formData, data);
+  var stack = [];
+
+  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 build(data, parentKey) {
+    if (utils.isPlainObject(data) || utils.isArray(data)) {
+      if (stack.indexOf(data) !== -1) {
+        throw Error('Circular reference detected in ' + parentKey);
+      }
+
+      stack.push(data);
+
+      utils.forEach(data, function each(value, key) {
+        if (utils.isUndefined(value)) return;
+
+        var fullKey = parentKey ? parentKey + '.' + key : key;
+        var arr;
+
+        if (value && !parentKey && typeof value === 'object') {
+          if (utils.endsWith(key, '{}')) {
+            // eslint-disable-next-line no-param-reassign
+            value = JSON.stringify(value);
+          } else if (utils.endsWith(key, '[]') && (arr = utils.toArray(value))) {
+            // eslint-disable-next-line func-names
+            arr.forEach(function(el) {
+              !utils.isUndefined(el) && formData.append(fullKey, convertValue(el));
+            });
+            return;
+          }
+        }
+
+        build(value, fullKey);
+      });
+
+      stack.pop();
+    } else {
+      formData.append(parentKey, convertValue(data));
+    }
+  }
+
+  build(obj);
 
   return formData;
-};
+}
+
+module.exports = toFormData;