url: use "empty" object for empty query strings

lib/url.js

@@ -60,6 +60,12 @@ const slashedProtocol = {
 };
 const querystring = require('querystring');
 
+// This constructor is used to store parsed query string values. Instantiating
+// this is faster than explicitly calling `Object.create(null)` to get a
+// "clean" empty object (tested with v8 v4.9).
+function ParsedQueryString() {}
+ParsedQueryString.prototype = Object.create(null);
+
 function urlParse(url, parseQueryString, slashesDenoteHost) {
  if (url instanceof Url) return url;
 
@@ -168,7 +174,7 @@ Url.prototype.parse = function(url, parseQueryString, slashesDenoteHost) {
  }
  } else if (parseQueryString) {
  this.search = '';
- this.query = {};
+ this.query = new ParsedQueryString();
  }
  return this;
  }
@@ -358,7 +364,7 @@ Url.prototype.parse = function(url, parseQueryString, slashesDenoteHost) {
  } else if (parseQueryString) {
  // no query string, but parseQueryString still requested
  this.search = '';
- this.query = {};
+ this.query = new ParsedQueryString();
  }
 
  var firstIdx = (questionIdx !== -1 &&

test/parallel/test-url.js

@@ -927,7 +927,7 @@ var parseTestsWithQueryString = {
  path: '/example',
  href: '/example'
  },
- '/example?query=value':{
+ '/example?query=value': {
  protocol: null,
  slashes: null,
  auth: null,
@@ -951,6 +951,8 @@ for (const u in parseTestsWithQueryString) {
  }
  }
 
+ assert.notStrictEqual(Object.getPrototypeOf(actual.query), Object.prototype);
+
  assert.deepEqual(actual, expected);
 }