es.regexp.constructor.js

var DESCRIPTORS = require('../internals/descriptors');
var global = require('../internals/global');
var isForced = require('../internals/is-forced');
var inheritIfRequired = require('../internals/inherit-if-required');
var defineProperty = require('../internals/object-define-property').f;
var getOwnPropertyNames = require('../internals/object-get-own-property-names').f;
var isRegExp = require('../internals/is-regexp');
var getFlags = require('../internals/regexp-flags');
var stickyHelpers = require('../internals/regexp-sticky-helpers');
var redefine = require('../internals/redefine');
var fails = require('../internals/fails');
var setInternalState = require('../internals/internal-state').set;
var setSpecies = require('../internals/set-species');
var wellKnownSymbol = require('../internals/well-known-symbol');

var MATCH = wellKnownSymbol('match');
var NativeRegExp = global.RegExp;
var RegExpPrototype = NativeRegExp.prototype;
var re1 = /a/g;
var re2 = /a/g;

// "new" should create a new object, old webkit bug
var CORRECT_NEW = new NativeRegExp(re1) !== re1;

var UNSUPPORTED_Y = stickyHelpers.UNSUPPORTED_Y;

var FORCED = DESCRIPTORS && isForced('RegExp', (!CORRECT_NEW || UNSUPPORTED_Y || fails(function () {
  re2[MATCH] = false;
  // RegExp constructor can alter flags and IsRegExp works correct with @@match
  return NativeRegExp(re1) != re1 || NativeRegExp(re2) == re2 || NativeRegExp(re1, 'i') != '/a/i';
})));

// `RegExp` constructor
// https://tc39.github.io/ecma262/#sec-regexp-constructor
if (FORCED) {
  var RegExpWrapper = function RegExp(pattern, flags) {
    var thisIsRegExp = this instanceof RegExpWrapper;
    var patternIsRegExp = isRegExp(pattern);
    var flagsAreUndefined = flags === undefined;
    var sticky;

    if (!thisIsRegExp && patternIsRegExp && pattern.constructor === RegExpWrapper && flagsAreUndefined) {
      return pattern;
    }

    if (CORRECT_NEW) {
      if (patternIsRegExp && !flagsAreUndefined) pattern = pattern.source;
    } else if (pattern instanceof RegExpWrapper) {
      if (flagsAreUndefined) flags = getFlags.call(pattern);
      pattern = pattern.source;
    }

    if (UNSUPPORTED_Y) {
      sticky = !!flags && flags.indexOf('y') > -1;
      if (sticky) flags = flags.replace(/y/g, '');
    }

    var result = inheritIfRequired(
      CORRECT_NEW ? new NativeRegExp(pattern, flags) : NativeRegExp(pattern, flags),
      thisIsRegExp ? this : RegExpPrototype,
      RegExpWrapper
    );

    if (UNSUPPORTED_Y && sticky) setInternalState(result, { sticky: sticky });

    return result;
  };
  var proxy = function (key) {
    key in RegExpWrapper || defineProperty(RegExpWrapper, key, {
      configurable: true,
      get: function () { return NativeRegExp[key]; },
      set: function (it) { NativeRegExp[key] = it; }
    });
  };
  var keys = getOwnPropertyNames(NativeRegExp);
  var index = 0;
  while (keys.length > index) proxy(keys[index++]);
  RegExpPrototype.constructor = RegExpWrapper;
  RegExpWrapper.prototype = RegExpPrototype;
  redefine(global, 'RegExp', RegExpWrapper);
}

// https://tc39.github.io/ecma262/#sec-get-regexp-@@species
setSpecies('RegExp');