Refactor and introduce deepMerge

lib/core/Axios.js

@@ -3,6 +3,7 @@
 var utils = require('./../utils');
 var InterceptorManager = require('./InterceptorManager');
 var dispatchRequest = require('./dispatchRequest');
+var mergeConfig = require('./mergeConfig');
 
 /**
  * Create a new instance of Axios
@@ -32,7 +33,7 @@ Axios.prototype.request = function request(config) {
     config = config || {};
   }
 
-  config = utils.mergeConfig(this.defaults, config);
+  config = mergeConfig(this.defaults, config);
   config.method = config.method ? config.method.toLowerCase() : 'get';
 
   // Hook up interceptors middleware

lib/core/mergeConfig.js

@@ -0,0 +1,44 @@
+'use strict';
+
+var utils = require('../utils');
+
+/**
+ * Config-specific merge-function which creates a new config-object
+ * based on given defaults and instance config.
+ *
+ * @param {Object} defaults Defaults
+ * @param {Object} instanceConfig Instance-specific config
+ * @returns {Object} New object resulting from merging instanceConfig to defaults
+ */
+module.exports = function mergeConfig(defaults, instanceConfig) {
+  // eslint-disable-next-line no-param-reassign
+  instanceConfig = instanceConfig || {};
+  var config = {};
+
+  utils.forEach(['url', 'method', 'params', 'data'], function valueFromInstanceConfig(prop) {
+    config[prop] = instanceConfig[prop];
+  });
+
+  utils.forEach(['headers', 'auth', 'proxy'], function mergeInstanceConfigWithDefaults(prop) {
+    if (typeof instanceConfig[prop] !== 'undefined') {
+      if (typeof instanceConfig[prop] === 'object') {
+        config[prop] = utils.deepMerge(defaults[prop], instanceConfig[prop]);
+      } else {
+        config[prop] = instanceConfig[prop];
+      }
+    } else if (typeof defaults[prop] !== 'undefined') {
+      config[prop] = utils.deepMerge(defaults[prop]);
+    }
+  });
+
+  utils.forEach([
+    'baseURL', 'transformRequest', 'transformResponse', 'paramsSerializer',
+    'timeout', 'withCredentials', 'adapter', 'responseType', 'xsrfCookieName',
+    'xsrfHeaderName', 'onUploadProgress', 'onDownloadProgress', 'maxContentLength',
+    'validateStatus', 'maxRedirects', 'httpAgent', 'httpsAgent', 'cancelToken'
+  ], function defaultToInstanceConfig(prop) {
+    config[prop] = typeof instanceConfig[prop] === 'undefined' ? defaults[prop] : instanceConfig[prop];
+  });
+
+  return config;
+};