core-js/internals/species-constructor.js

'use strict';
var anObject = require('../internals/an-object');
var aConstructor = require('../internals/a-constructor');
var isNullOrUndefined = require('../internals/is-null-or-undefined');
var wellKnownSymbol = require('../internals/well-known-symbol');

var SPECIES = wellKnownSymbol('species');

// `SpeciesConstructor` abstract operation
// https://tc39.es/ecma262/#sec-speciesconstructor
module.exports = function (O, defaultConstructor) {
  var C = anObject(O).constructor;
  var S;
  return C === undefined || isNullOrUndefined(S = anObject(C)[SPECIES]) ? defaultConstructor : aConstructor(S);
};