var wellKnownSymbol = require('../internals/well-known-symbol'); var create = require('../internals/object-create'); var definePropertyModule = require('../internals/object-define-property'); var UNSCOPABLES = wellKnownSymbol('unscopables'); var ArrayPrototype = Array.prototype; // Array.prototype[@@unscopables] // https://tc39.github.io/ecma262/#sec-array.prototype-@@unscopables if (ArrayPrototype[UNSCOPABLES] == undefined) { definePropertyModule.f(ArrayPrototype, UNSCOPABLES, { configurable: true, value: create(null) }); } // add a key to Array.prototype[@@unscopables] module.exports = function (key) { ArrayPrototype[UNSCOPABLES][key] = true; };