add-to-unscopables.js
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add-to-unscopables.js
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	var wellKnownSymbol = require('../internals/well-known-symbol');
	var create = require('../internals/object-create');
	var defineProperty = require('../internals/object-define-property').f;

	var UNSCOPABLES = wellKnownSymbol('unscopables');
	var ArrayPrototype = Array.prototype;

	// Array.prototype[@@unscopables]
	// https://tc39.es/ecma262/#sec-array.prototype-@@unscopables
	if (ArrayPrototype[UNSCOPABLES] == undefined) {
	defineProperty(ArrayPrototype, UNSCOPABLES, {
	configurable: true,
	value: create(null)
	});
	}

	// add a key to Array.prototype[@@unscopables]
	module.exports = function (key) {
	ArrayPrototype[UNSCOPABLES][key] = true;
	};