refactor: modernize utils and xhr adapter using ES6 features (#10588)

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

lib/adapters/xhr.js

@@ -91,7 +91,7 @@ export default isXHRAdapterSupported &&
           // will return status as 0 even though it's a successful request
           if (
             request.status === 0 &&
-            !(request.responseURL && request.responseURL.indexOf('file:') === 0)
+            !(request.responseURL && request.responseURL.startsWith('file:'))
           ) {
             return;
           }
@@ -205,7 +205,7 @@ export default isXHRAdapterSupported &&
 
       const protocol = parseProtocol(_config.url);
 
-      if (protocol && platform.protocols.indexOf(protocol) === -1) {
+      if (protocol && !platform.protocols.includes(protocol)) {
         reject(
           new AxiosError(
             'Unsupported protocol ' + protocol + ':',

lib/utils.js

@@ -401,7 +401,7 @@ const isContextDefined = (context) => !isUndefined(context) && context !== _glob
  *
  * @returns {Object} Result of all merge properties
  */
-function merge(/* obj1, obj2, obj3, ... */) {
+function merge(...objs) {
   const { caseless, skipUndefined } = (isContextDefined(this) && this) || {};
   const result = {};
   const assignValue = (val, key) => {
@@ -422,8 +422,8 @@ function merge(/* obj1, obj2, obj3, ... */) {
     }
   };
 
-  for (let i = 0, l = arguments.length; i < l; i++) {
-    arguments[i] && forEach(arguments[i], assignValue);
+  for (let i = 0, l = objs.length; i < l; i++) {
+    objs[i] && forEach(objs[i], assignValue);
   }
   return result;
 }
@@ -677,7 +677,7 @@ const reduceDescriptors = (obj, reducer) => {
 const freezeMethods = (obj) => {
   reduceDescriptors(obj, (descriptor, name) => {
     // skip restricted props in strict mode
-    if (isFunction(obj) && ['arguments', 'caller', 'callee'].indexOf(name) !== -1) {
+    if (isFunction(obj) && ['arguments', 'caller', 'callee'].includes(name)) {
       return false;
     }