object-create.js

var anObject = require('../internals/an-object');
var defineProperties = require('../internals/object-define-properties');
var enumBugKeys = require('../internals/enum-bug-keys');
var hiddenKeys = require('../internals/hidden-keys');
var html = require('../internals/html');
var documentCreateElement = require('../internals/document-create-element');
var sharedKey = require('../internals/shared-key');

var GT = '>';
var LT = '<';
var PROTOTYPE = 'prototype';
var SCRIPT = 'script';
var IE_PROTO = sharedKey('IE_PROTO');

var EmptyConstructor = function () { /* empty */ };

var scriptTag = function (content) {
  return LT + SCRIPT + GT + content + LT + '/' + SCRIPT + GT;
};

// Create object with fake `null` prototype: use ActiveX Object with cleared prototype
var NullProtoObjectViaActiveX = function (activeXDocument) {
  activeXDocument.write(scriptTag(''));
  activeXDocument.close();
  var temp = activeXDocument.parentWindow.Object;
  activeXDocument = null; // avoid memory leak
  return temp;
};

// Create object with fake `null` prototype: use iframe Object with cleared prototype
var NullProtoObjectViaIFrame = function () {
  // Thrash, waste and sodomy: IE GC bug
  var iframe = documentCreateElement('iframe');
  var JS = 'java' + SCRIPT + ':';
  var iframeDocument;
  iframe.style.display = 'none';
  html.appendChild(iframe);
  // https://github.com/zloirock/core-js/issues/475
  iframe.src = String(JS);
  iframeDocument = iframe.contentWindow.document;
  iframeDocument.open();
  iframeDocument.write(scriptTag('document.F=Object'));
  iframeDocument.close();
  return iframeDocument.F;
};

// Check for document.domain and active x support
// No need to use active x approach when document.domain is not set
// see https://github.com/es-shims/es5-shim/issues/150
// variation of https://github.com/kitcambridge/es5-shim/commit/4f738ac066346
// avoid IE GC bug
var activeXDocument;
var NullProtoObject = function () {
  try {
    /* global ActiveXObject -- old IE */
    activeXDocument = document.domain && new ActiveXObject('htmlfile');
  } catch (error) { /* ignore */ }
  NullProtoObject = activeXDocument ? NullProtoObjectViaActiveX(activeXDocument) : NullProtoObjectViaIFrame();
  var length = enumBugKeys.length;
  while (length--) delete NullProtoObject[PROTOTYPE][enumBugKeys[length]];
  return NullProtoObject();
};

hiddenKeys[IE_PROTO] = true;

// `Object.create` method
// https://tc39.es/ecma262/#sec-object.create
module.exports = Object.create || function create(O, Properties) {
  var result;
  if (O !== null) {
    EmptyConstructor[PROTOTYPE] = anObject(O);
    result = new EmptyConstructor();
    EmptyConstructor[PROTOTYPE] = null;
    // add "__proto__" for Object.getPrototypeOf polyfill
    result[IE_PROTO] = O;
  } else result = NullProtoObject();
  return Properties === undefined ? result : defineProperties(result, Properties);
};