lib: use Object.create(null) directly

After V8 5.6, using Object.create(null) directly is now faster than
using a constructor for map-like objects.

PR-URL: https://github.com/nodejs/node/pull/11930
Refs: https://github.com/emberjs/ember.js/issues/15001
Refs: https://crrev.com/532c16eca071df3ec8eed394dcebb932ef584ee6
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/_http_outgoing.js

@@ -31,7 +31,6 @@ const common = require('_http_common');
 const checkIsHttpToken = common._checkIsHttpToken;
 const checkInvalidHeaderChar = common._checkInvalidHeaderChar;
 const outHeadersKey = require('internal/http').outHeadersKey;
-const StorageObject = require('internal/querystring').StorageObject;
 
 const CRLF = common.CRLF;
 const debug = common.debug;
@@ -143,7 +142,7 @@ Object.defineProperty(OutgoingMessage.prototype, '_headerNames', {
   get: function() {
     const headers = this[outHeadersKey];
     if (headers) {
-      const out = new StorageObject();
+      const out = Object.create(null);
       const keys = Object.keys(headers);
       for (var i = 0; i < keys.length; ++i) {
         const key = keys[i];
@@ -552,7 +551,7 @@ OutgoingMessage.prototype.getHeaderNames = function getHeaderNames() {
 // Returns a shallow copy of the current outgoing headers.
 OutgoingMessage.prototype.getHeaders = function getHeaders() {
   const headers = this[outHeadersKey];
-  const ret = new StorageObject();
+  const ret = Object.create(null);
   if (headers) {
     const keys = Object.keys(headers);
     for (var i = 0; i < keys.length; ++i) {

lib/events.js

@@ -23,12 +23,6 @@
 
 var domain;
 
-// This constructor is used to store event handlers. Instantiating this is
-// faster than explicitly calling `Object.create(null)` to get a "clean" empty
-// object (tested with v8 v4.9).
-function EventHandlers() {}
-EventHandlers.prototype = Object.create(null);
-
 function EventEmitter() {
   EventEmitter.init.call(this);
 }
@@ -75,7 +69,7 @@ EventEmitter.init = function() {
   }
 
   if (!this._events || this._events === Object.getPrototypeOf(this)._events) {
-    this._events = new EventHandlers();
+    this._events = Object.create(null);
     this._eventsCount = 0;
   }
 
@@ -245,7 +239,7 @@ function _addListener(target, type, listener, prepend) {
 
   events = target._events;
   if (!events) {
-    events = target._events = new EventHandlers();
+    events = target._events = Object.create(null);
     target._eventsCount = 0;
   } else {
     // To avoid recursion in the case that type === "newListener"! Before
@@ -360,7 +354,7 @@ EventEmitter.prototype.removeListener =
 
       if (list === listener || list.listener === listener) {
         if (--this._eventsCount === 0)
-          this._events = new EventHandlers();
+          this._events = Object.create(null);
         else {
           delete events[type];
           if (events.removeListener)
@@ -383,7 +377,7 @@ EventEmitter.prototype.removeListener =
         if (list.length === 1) {
           list[0] = undefined;
           if (--this._eventsCount === 0) {
-            this._events = new EventHandlers();
+            this._events = Object.create(null);
             return this;
           } else {
             delete events[type];
@@ -412,11 +406,11 @@ EventEmitter.prototype.removeAllListeners =
       // not listening for removeListener, no need to emit
       if (!events.removeListener) {
         if (arguments.length === 0) {
-          this._events = new EventHandlers();
+          this._events = Object.create(null);
           this._eventsCount = 0;
         } else if (events[type]) {
           if (--this._eventsCount === 0)
-            this._events = new EventHandlers();
+            this._events = Object.create(null);
           else
             delete events[type];
         }
@@ -432,7 +426,7 @@ EventEmitter.prototype.removeAllListeners =
           this.removeAllListeners(key);
         }
         this.removeAllListeners('removeListener');
-        this._events = new EventHandlers();
+        this._events = Object.create(null);
         this._eventsCount = 0;
         return this;
       }

lib/fs.js

@@ -43,7 +43,6 @@ const internalUtil = require('internal/util');
 const assertEncoding = internalFS.assertEncoding;
 const stringToFlags = internalFS.stringToFlags;
 const getPathFromURL = internalURL.getPathFromURL;
-const { StorageObject } = require('internal/querystring');
 
 Object.defineProperty(exports, 'constants', {
   configurable: false,
@@ -1560,7 +1559,7 @@ if (isWindows) {
   nextPart = function nextPart(p, i) { return p.indexOf('/', i); };
 }
 
-const emptyObj = new StorageObject();
+const emptyObj = Object.create(null);
 fs.realpathSync = function realpathSync(p, options) {
   if (!options)
     options = emptyObj;
@@ -1580,8 +1579,8 @@ fs.realpathSync = function realpathSync(p, options) {
     return maybeCachedResult;
   }
 
-  const seenLinks = new StorageObject();
-  const knownHard = new StorageObject();
+  const seenLinks = Object.create(null);
+  const knownHard = Object.create(null);
   const original = p;
 
   // current character position in p
@@ -1700,8 +1699,8 @@ fs.realpath = function realpath(p, options, callback) {
     return;
   p = pathModule.resolve(p);
 
-  const seenLinks = new StorageObject();
-  const knownHard = new StorageObject();
+  const seenLinks = Object.create(null);
+  const knownHard = Object.create(null);
 
   // current character position in p
   var pos;

lib/internal/querystring.js

@@ -23,13 +23,7 @@ const isHexTable = [
   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0  // ... 256
 ];
 
-// Instantiating this is faster than explicitly calling `Object.create(null)`
-// to get a "clean" empty object (tested with v8 v4.9).
-function StorageObject() {}
-StorageObject.prototype = Object.create(null);
-
 module.exports = {
   hexTable,
-  isHexTable,
-  StorageObject
+  isHexTable
 };

lib/querystring.js

@@ -25,7 +25,6 @@
 
 const { Buffer } = require('buffer');
 const {
-  StorageObject,
   hexTable,
   isHexTable
 } = require('internal/querystring');
@@ -281,7 +280,7 @@ const defEqCodes = [61]; // =
 
 // Parse a key/val string.
 function parse(qs, sep, eq, options) {
-  const obj = new StorageObject();
+  const obj = Object.create(null);
 
   if (typeof qs !== 'string' || qs.length === 0) {
     return obj;

lib/url.js

@@ -23,7 +23,7 @@
 
 const { toASCII } = process.binding('config').hasIntl ?
   process.binding('icu') : require('punycode');
-const { StorageObject, hexTable } = require('internal/querystring');
+const { hexTable } = require('internal/querystring');
 const internalUrl = require('internal/url');
 exports.parse = urlParse;
 exports.resolve = urlResolve;
@@ -197,7 +197,7 @@ Url.prototype.parse = function(url, parseQueryString, slashesDenoteHost) {
         }
       } else if (parseQueryString) {
         this.search = '';
-        this.query = new StorageObject();
+        this.query = Object.create(null);
       }
       return this;
     }
@@ -390,7 +390,7 @@ Url.prototype.parse = function(url, parseQueryString, slashesDenoteHost) {
   } else if (parseQueryString) {
     // no query string, but parseQueryString still requested
     this.search = '';
-    this.query = new StorageObject();
+    this.query = Object.create(null);
   }
 
   var firstIdx = (questionIdx !== -1 &&