use hasOwnProperty in check against files/fields (#522)

* use hasOwnProperty in check against files/fields

* Update CHANGELOG.md

CHANGELOG.md

@@ -6,6 +6,7 @@
  * throw error during data parsing ([#513](https://github.com/node-formidable/node-formidable/pull/513))
  * Array parameters support (array-like fields) ([#380](https://github.com/node-formidable/node-formidable/pull/380), [#340](https://github.com/node-formidable/node-formidable/pull/340), [#367](https://github.com/node-formidable/node-formidable/pull/367))
  * possible partial fix of [#386](https://github.com/node-formidable/node-formidable/pull/386) with #380 (need tests and better implementation)
+ * use hasOwnProperty in check against files/fields ([#522](https://github.com/node-formidable/node-formidable/pull/522))
 
 ### v1.2.1 (2018-03-20)
 

lib/incoming_form.js

@@ -14,6 +14,10 @@ var util = require('util'),
     Stream = require('stream').Stream,
     os = require('os');
 
+function hasOwnProp(obj, key) {
+  return Object.prototype.hasOwnProperty.call(obj, key);
+}
+
 function IncomingForm(opts) {
   if (!(this instanceof IncomingForm)) return new IncomingForm(opts);
   EventEmitter.call(this);
@@ -86,7 +90,7 @@ IncomingForm.prototype.parse = function(req, cb) {
       .on('field', function(name, value) {
         if (this.multiples && name.slice(-2) === '[]') {
           var realName = name.slice(0, name.length - 2);
-          if (realName in fields) {
+          if (hasOwnProp(fields, realName)) {
             if (!Array.isArray(fields[realName])) {
               fields[realName] = [fields[realName]];
             }
@@ -100,7 +104,7 @@ IncomingForm.prototype.parse = function(req, cb) {
       })
       .on('file', function(name, file) {
         if (this.multiples) {
-          if (files[name]) {
+          if (hasOwnProp(files, name)) {
             if (!Array.isArray(files[name])) {
               files[name] = [files[name]];
             }