'use strict';

var has = require('has');
var toPrimitive = require('es-to-primitive/es6');
var keys = require('object-keys');
var inspect = require('object-inspect');

var GetIntrinsic = require('./GetIntrinsic');

var $TypeError = GetIntrinsic('%TypeError%');
var $RangeError = GetIntrinsic('%RangeError%');
var $SyntaxError = GetIntrinsic('%SyntaxError%');
var $Array = GetIntrinsic('%Array%');
var $ArrayPrototype = $Array.prototype;
var $String = GetIntrinsic('%String%');
var $Object = GetIntrinsic('%Object%');
var $Number = GetIntrinsic('%Number%');
var $Symbol = GetIntrinsic('%Symbol%', true);
var $RegExp = GetIntrinsic('%RegExp%');
var $Date = GetIntrinsic('%Date%');
var $Function = GetIntrinsic('%Function%');
var $preventExtensions = $Object.preventExtensions;

var hasSymbols = require('has-symbols')();

var assertRecord = require('./helpers/assertRecord');
var $isNaN = require('./helpers/isNaN');
var $isFinite = require('./helpers/isFinite');
var MAX_ARRAY_LENGTH = Math.pow(2, 32) - 1;
var MAX_SAFE_INTEGER = require('./helpers/maxSafeInteger');

var assign = require('./helpers/assign');
var sign = require('./helpers/sign');
var mod = require('./helpers/mod');
var isPrimitive = require('./helpers/isPrimitive');
var forEach = require('./helpers/forEach');
var every = require('./helpers/every');
var isSamePropertyDescriptor = require('./helpers/isSamePropertyDescriptor');
var isPropertyDescriptor = require('./helpers/isPropertyDescriptor');
var parseInteger = parseInt;
var callBound = require('./helpers/callBound');
var regexTester = require('./helpers/regexTester');
var getIteratorMethod = require('./helpers/getIteratorMethod');
var getSymbolDescription = require('./helpers/getSymbolDescription');

var $PromiseThen = callBound('Promise.prototype.then', true);
var arraySlice = callBound('Array.prototype.slice');
var strSlice = callBound('String.prototype.slice');
var $indexOf = callBound('Array.prototype.indexOf');
var $push = callBound('Array.prototype.push');

var isBinary = regexTester(/^0b[01]+$/i);
var isOctal = regexTester(/^0o[0-7]+$/i);
var isDigit = regexTester(/^[0-9]$/);
var regexExec = callBound('RegExp.prototype.exec');
var nonWS = ['\u0085', '\u200b', '\ufffe'].join('');
var nonWSregex = new $RegExp('[' + nonWS + ']', 'g');
var hasNonWS = regexTester(nonWSregex);
var isInvalidHexLiteral = regexTester(/^[-+]0x[0-9a-f]+$/i);
var $charCodeAt = callBound('String.prototype.charCodeAt');
var $isEnumerable = callBound('Object.prototype.propertyIsEnumerable');

var toStr = callBound('Object.prototype.toString');

var $NumberValueOf = callBound('Number.prototype.valueOf');
var $BooleanValueOf = callBound('Boolean.prototype.valueOf');
var $StringValueOf = callBound('String.prototype.valueOf');
var $DateValueOf = callBound('Date.prototype.valueOf');
var $SymbolToString = callBound('Symbol.prototype.toString', true);

var $floor = Math.floor;
var $abs = Math.abs;

var $ObjectCreate = $Object.create;
var $gOPD = $Object.getOwnPropertyDescriptor;
var $gOPN = $Object.getOwnPropertyNames;
var $gOPS = $Object.getOwnPropertySymbols;
var $isExtensible = $Object.isExtensible;
var $defineProperty = $Object.defineProperty;
var $setProto = require('./helpers/setProto');

var DefineOwnProperty = function DefineOwnProperty(ES, O, P, desc) {
	if (!$defineProperty) {
		if (!ES.IsDataDescriptor(desc)) {
			// ES3 does not support getters/setters
			return false;
		}
		if (!desc['[[Configurable]]'] || !desc['[[Writable]]']) {
			return false;
		}

		// fallback for ES3
		if (P in O && $isEnumerable(O, P) !== !!desc['[[Enumerable]]']) {
			// a non-enumerable existing property
			return false;
		}

		// property does not exist at all, or exists but is enumerable
		var V = desc['[[Value]]'];
		O[P] = V; // will use [[Define]]
		return ES.SameValue(O[P], V);
	}
	$defineProperty(O, P, ES.FromPropertyDescriptor(desc));
	return true;
};

// whitespace from: https://es5.github.io/#x15.5.4.20
// implementation from https://github.com/es-shims/es5-shim/blob/v3.4.0/es5-shim.js#L1304-L1324
var ws = [
	'\x09\x0A\x0B\x0C\x0D\x20\xA0\u1680\u180E\u2000\u2001\u2002\u2003',
	'\u2004\u2005\u2006\u2007\u2008\u2009\u200A\u202F\u205F\u3000\u2028',
	'\u2029\uFEFF'
].join('');
var trimRegex = new RegExp('(^[' + ws + ']+)|([' + ws + ']+$)', 'g');
var $replace = callBound('String.prototype.replace');
var trim = function (value) {
	return $replace(value, trimRegex, '');
};

var ES5 = require('./es5');

var hasRegExpMatcher = require('is-regex');

// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-abstract-operations
var ES6 = assign(assign({}, ES5), {

	// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-call-f-v-args
	Call: function Call(F, V) {
		var args = arguments.length > 2 ? arguments[2] : [];
		if (!this.IsCallable(F)) {
			throw new $TypeError(inspect(F) + ' is not a function');
		}
		return F.apply(V, args);
	},

	// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-toprimitive
	ToPrimitive: toPrimitive,

	// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-toboolean
	// ToBoolean: ES5.ToBoolean,

	// https://ecma-international.org/ecma-262/6.0/#sec-tonumber
	ToNumber: function ToNumber(argument) {
		var value = isPrimitive(argument) ? argument : toPrimitive(argument, $Number);
		if (typeof value === 'symbol') {
			throw new $TypeError('Cannot convert a Symbol value to a number');
		}
		if (typeof value === 'string') {
			if (isBinary(value)) {
				return this.ToNumber(parseInteger(strSlice(value, 2), 2));
			} else if (isOctal(value)) {
				return this.ToNumber(parseInteger(strSlice(value, 2), 8));
			} else if (hasNonWS(value) || isInvalidHexLiteral(value)) {
				return NaN;
			} else {
				var trimmed = trim(value);
				if (trimmed !== value) {
					return this.ToNumber(trimmed);
				}
			}
		}
		return $Number(value);
	},

	// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-tointeger
	// ToInteger: ES5.ToNumber,

	// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-toint32
	// ToInt32: ES5.ToInt32,

	// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-touint32
	// ToUint32: ES5.ToUint32,

	// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-toint16
	ToInt16: function ToInt16(argument) {
		var int16bit = this.ToUint16(argument);
		return int16bit >= 0x8000 ? int16bit - 0x10000 : int16bit;
	},

	// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-touint16
	// ToUint16: ES5.ToUint16,

	// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-toint8
	ToInt8: function ToInt8(argument) {
		var int8bit = this.ToUint8(argument);
		return int8bit >= 0x80 ? int8bit - 0x100 : int8bit;
	},

	// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-touint8
	ToUint8: function ToUint8(argument) {
		var number = this.ToNumber(argument);
		if ($isNaN(number) || number === 0 || !$isFinite(number)) { return 0; }
		var posInt = sign(number) * $floor($abs(number));
		return mod(posInt, 0x100);
	},

	// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-touint8clamp
	ToUint8Clamp: function ToUint8Clamp(argument) {
		var number = this.ToNumber(argument);
		if ($isNaN(number) || number <= 0) { return 0; }
		if (number >= 0xFF) { return 0xFF; }
		var f = $floor(argument);
		if (f + 0.5 < number) { return f + 1; }
		if (number < f + 0.5) { return f; }
		if (f % 2 !== 0) { return f + 1; }
		return f;
	},

	// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-tostring
	ToString: function ToString(argument) {
		if (typeof argument === 'symbol') {
			throw new $TypeError('Cannot convert a Symbol value to a string');
		}
		return $String(argument);
	},

	// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-toobject
	ToObject: function ToObject(value) {
		this.RequireObjectCoercible(value);
		return $Object(value);
	},

	// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-topropertykey
	ToPropertyKey: function ToPropertyKey(argument) {
		var key = this.ToPrimitive(argument, $String);
		return typeof key === 'symbol' ? key : this.ToString(key);
	},

	// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-tolength
	ToLength: function ToLength(argument) {
		var len = this.ToInteger(argument);
		if (len <= 0) { return 0; } // includes converting -0 to +0
		if (len > MAX_SAFE_INTEGER) { return MAX_SAFE_INTEGER; }
		return len;
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-canonicalnumericindexstring
	CanonicalNumericIndexString: function CanonicalNumericIndexString(argument) {
		if (toStr(argument) !== '[object String]') {
			throw new $TypeError('must be a string');
		}
		if (argument === '-0') { return -0; }
		var n = this.ToNumber(argument);
		if (this.SameValue(this.ToString(n), argument)) { return n; }
		return void 0;
	},

	// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-requireobjectcoercible
	RequireObjectCoercible: ES5.CheckObjectCoercible,

	// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-isarray
	IsArray: $Array.isArray || function IsArray(argument) {
		return toStr(argument) === '[object Array]';
	},

	// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-iscallable
	// IsCallable: ES5.IsCallable,

	// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-isconstructor
	IsConstructor: function IsConstructor(argument) {
		return typeof argument === 'function' && !!argument.prototype; // unfortunately there's no way to truly check this without try/catch `new argument` or Proxy
	},

	// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-isextensible-o
	IsExtensible: $preventExtensions
		? function IsExtensible(obj) {
			if (isPrimitive(obj)) {
				return false;
			}
			return $isExtensible(obj);
		}
		: function isExtensible(obj) { return true; }, // eslint-disable-line no-unused-vars

	// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-isinteger
	IsInteger: function IsInteger(argument) {
		if (typeof argument !== 'number' || $isNaN(argument) || !$isFinite(argument)) {
			return false;
		}
		var abs = $abs(argument);
		return $floor(abs) === abs;
	},

	// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-ispropertykey
	IsPropertyKey: function IsPropertyKey(argument) {
		return typeof argument === 'string' || typeof argument === 'symbol';
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-isregexp
	IsRegExp: function IsRegExp(argument) {
		if (!argument || typeof argument !== 'object') {
			return false;
		}
		if (hasSymbols) {
			var isRegExp = argument[$Symbol.match];
			if (typeof isRegExp !== 'undefined') {
				return ES5.ToBoolean(isRegExp);
			}
		}
		return hasRegExpMatcher(argument);
	},

	// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-samevalue
	// SameValue: ES5.SameValue,

	// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-samevaluezero
	SameValueZero: function SameValueZero(x, y) {
		return (x === y) || ($isNaN(x) && $isNaN(y));
	},

	/**
	 * 7.3.2 GetV (V, P)
	 * 1. Assert: IsPropertyKey(P) is true.
	 * 2. Let O be ToObject(V).
	 * 3. ReturnIfAbrupt(O).
	 * 4. Return O.[[Get]](P, V).
	 */
	GetV: function GetV(V, P) {
		// 7.3.2.1
		if (!this.IsPropertyKey(P)) {
			throw new $TypeError('Assertion failed: IsPropertyKey(P) is not true');
		}

		// 7.3.2.2-3
		var O = this.ToObject(V);

		// 7.3.2.4
		return O[P];
	},

	/**
	 * 7.3.9 - https://ecma-international.org/ecma-262/6.0/#sec-getmethod
	 * 1. Assert: IsPropertyKey(P) is true.
	 * 2. Let func be GetV(O, P).
	 * 3. ReturnIfAbrupt(func).
	 * 4. If func is either undefined or null, return undefined.
	 * 5. If IsCallable(func) is false, throw a TypeError exception.
	 * 6. Return func.
	 */
	GetMethod: function GetMethod(O, P) {
		// 7.3.9.1
		if (!this.IsPropertyKey(P)) {
			throw new $TypeError('Assertion failed: IsPropertyKey(P) is not true');
		}

		// 7.3.9.2
		var func = this.GetV(O, P);

		// 7.3.9.4
		if (func == null) {
			return void 0;
		}

		// 7.3.9.5
		if (!this.IsCallable(func)) {
			throw new $TypeError(P + 'is not a function');
		}

		// 7.3.9.6
		return func;
	},

	/**
	 * 7.3.1 Get (O, P) - https://ecma-international.org/ecma-262/6.0/#sec-get-o-p
	 * 1. Assert: Type(O) is Object.
	 * 2. Assert: IsPropertyKey(P) is true.
	 * 3. Return O.[[Get]](P, O).
	 */
	Get: function Get(O, P) {
		// 7.3.1.1
		if (this.Type(O) !== 'Object') {
			throw new $TypeError('Assertion failed: Type(O) is not Object');
		}
		// 7.3.1.2
		if (!this.IsPropertyKey(P)) {
			throw new $TypeError('Assertion failed: IsPropertyKey(P) is not true, got ' + inspect(P));
		}
		// 7.3.1.3
		return O[P];
	},

	Type: function Type(x) {
		if (typeof x === 'symbol') {
			return 'Symbol';
		}
		return ES5.Type(x);
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-speciesconstructor
	SpeciesConstructor: function SpeciesConstructor(O, defaultConstructor) {
		if (this.Type(O) !== 'Object') {
			throw new $TypeError('Assertion failed: Type(O) is not Object');
		}
		var C = O.constructor;
		if (typeof C === 'undefined') {
			return defaultConstructor;
		}
		if (this.Type(C) !== 'Object') {
			throw new $TypeError('O.constructor is not an Object');
		}
		var S = hasSymbols && $Symbol.species ? C[$Symbol.species] : void 0;
		if (S == null) {
			return defaultConstructor;
		}
		if (this.IsConstructor(S)) {
			return S;
		}
		throw new $TypeError('no constructor found');
	},

	// https://www.ecma-international.org/ecma-262/6.0/#sec-frompropertydescriptor
	FromPropertyDescriptor: function FromPropertyDescriptor(Desc) {
		if (typeof Desc === 'undefined') {
			return Desc;
		}

		assertRecord(this, 'Property Descriptor', 'Desc', Desc);

		var obj = {};
		if ('[[Value]]' in Desc) {
			obj.value = Desc['[[Value]]'];
		}
		if ('[[Writable]]' in Desc) {
			obj.writable = Desc['[[Writable]]'];
		}
		if ('[[Get]]' in Desc) {
			obj.get = Desc['[[Get]]'];
		}
		if ('[[Set]]' in Desc) {
			obj.set = Desc['[[Set]]'];
		}
		if ('[[Enumerable]]' in Desc) {
			obj.enumerable = Desc['[[Enumerable]]'];
		}
		if ('[[Configurable]]' in Desc) {
			obj.configurable = Desc['[[Configurable]]'];
		}
		return obj;
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-completepropertydescriptor
	CompletePropertyDescriptor: function CompletePropertyDescriptor(Desc) {
		assertRecord(this, 'Property Descriptor', 'Desc', Desc);

		if (this.IsGenericDescriptor(Desc) || this.IsDataDescriptor(Desc)) {
			if (!has(Desc, '[[Value]]')) {
				Desc['[[Value]]'] = void 0;
			}
			if (!has(Desc, '[[Writable]]')) {
				Desc['[[Writable]]'] = false;
			}
		} else {
			if (!has(Desc, '[[Get]]')) {
				Desc['[[Get]]'] = void 0;
			}
			if (!has(Desc, '[[Set]]')) {
				Desc['[[Set]]'] = void 0;
			}
		}
		if (!has(Desc, '[[Enumerable]]')) {
			Desc['[[Enumerable]]'] = false;
		}
		if (!has(Desc, '[[Configurable]]')) {
			Desc['[[Configurable]]'] = false;
		}
		return Desc;
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-set-o-p-v-throw
	Set: function Set(O, P, V, Throw) {
		if (this.Type(O) !== 'Object') {
			throw new $TypeError('O must be an Object');
		}
		if (!this.IsPropertyKey(P)) {
			throw new $TypeError('P must be a Property Key');
		}
		if (this.Type(Throw) !== 'Boolean') {
			throw new $TypeError('Throw must be a Boolean');
		}
		if (Throw) {
			O[P] = V;
			return true;
		} else {
			try {
				O[P] = V;
			} catch (e) {
				return false;
			}
		}
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-hasownproperty
	HasOwnProperty: function HasOwnProperty(O, P) {
		if (this.Type(O) !== 'Object') {
			throw new $TypeError('O must be an Object');
		}
		if (!this.IsPropertyKey(P)) {
			throw new $TypeError('P must be a Property Key');
		}
		return has(O, P);
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-hasproperty
	HasProperty: function HasProperty(O, P) {
		if (this.Type(O) !== 'Object') {
			throw new $TypeError('O must be an Object');
		}
		if (!this.IsPropertyKey(P)) {
			throw new $TypeError('P must be a Property Key');
		}
		return P in O;
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-isconcatspreadable
	IsConcatSpreadable: function IsConcatSpreadable(O) {
		if (this.Type(O) !== 'Object') {
			return false;
		}
		if (hasSymbols && typeof $Symbol.isConcatSpreadable === 'symbol') {
			var spreadable = this.Get(O, Symbol.isConcatSpreadable);
			if (typeof spreadable !== 'undefined') {
				return this.ToBoolean(spreadable);
			}
		}
		return this.IsArray(O);
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-invoke
	Invoke: function Invoke(O, P) {
		if (!this.IsPropertyKey(P)) {
			throw new $TypeError('P must be a Property Key');
		}
		var argumentsList = arraySlice(arguments, 2);
		var func = this.GetV(O, P);
		return this.Call(func, O, argumentsList);
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-getiterator
	GetIterator: function GetIterator(obj, method) {
		var actualMethod = method;
		if (arguments.length < 2) {
			actualMethod = getIteratorMethod(this, obj);
		}
		var iterator = this.Call(actualMethod, obj);
		if (this.Type(iterator) !== 'Object') {
			throw new $TypeError('iterator must return an object');
		}

		return iterator;
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-iteratornext
	IteratorNext: function IteratorNext(iterator, value) {
		var result = this.Invoke(iterator, 'next', arguments.length < 2 ? [] : [value]);
		if (this.Type(result) !== 'Object') {
			throw new $TypeError('iterator next must return an object');
		}
		return result;
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-iteratorcomplete
	IteratorComplete: function IteratorComplete(iterResult) {
		if (this.Type(iterResult) !== 'Object') {
			throw new $TypeError('Assertion failed: Type(iterResult) is not Object');
		}
		return this.ToBoolean(this.Get(iterResult, 'done'));
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-iteratorvalue
	IteratorValue: function IteratorValue(iterResult) {
		if (this.Type(iterResult) !== 'Object') {
			throw new $TypeError('Assertion failed: Type(iterResult) is not Object');
		}
		return this.Get(iterResult, 'value');
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-iteratorstep
	IteratorStep: function IteratorStep(iterator) {
		var result = this.IteratorNext(iterator);
		var done = this.IteratorComplete(result);
		return done === true ? false : result;
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-iteratorclose
	IteratorClose: function IteratorClose(iterator, completion) {
		if (this.Type(iterator) !== 'Object') {
			throw new $TypeError('Assertion failed: Type(iterator) is not Object');
		}
		if (!this.IsCallable(completion)) {
			throw new $TypeError('Assertion failed: completion is not a thunk for a Completion Record');
		}
		var completionThunk = completion;

		var iteratorReturn = this.GetMethod(iterator, 'return');

		if (typeof iteratorReturn === 'undefined') {
			return completionThunk();
		}

		var completionRecord;
		try {
			var innerResult = this.Call(iteratorReturn, iterator, []);
		} catch (e) {
			// if we hit here, then "e" is the innerResult completion that needs re-throwing

			// if the completion is of type "throw", this will throw.
			completionRecord = completionThunk();
			completionThunk = null; // ensure it's not called twice.

			// if not, then return the innerResult completion
			throw e;
		}
		completionRecord = completionThunk(); // if innerResult worked, then throw if the completion does
		completionThunk = null; // ensure it's not called twice.

		if (this.Type(innerResult) !== 'Object') {
			throw new $TypeError('iterator .return must return an object');
		}

		return completionRecord;
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-createiterresultobject
	CreateIterResultObject: function CreateIterResultObject(value, done) {
		if (this.Type(done) !== 'Boolean') {
			throw new $TypeError('Assertion failed: Type(done) is not Boolean');
		}
		return {
			value: value,
			done: done
		};
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-regexpexec
	RegExpExec: function RegExpExec(R, S) {
		if (this.Type(R) !== 'Object') {
			throw new $TypeError('R must be an Object');
		}
		if (this.Type(S) !== 'String') {
			throw new $TypeError('S must be a String');
		}
		var exec = this.Get(R, 'exec');
		if (this.IsCallable(exec)) {
			var result = this.Call(exec, R, [S]);
			if (result === null || this.Type(result) === 'Object') {
				return result;
			}
			throw new $TypeError('"exec" method must return `null` or an Object');
		}
		return regexExec(R, S);
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-arrayspeciescreate
	ArraySpeciesCreate: function ArraySpeciesCreate(originalArray, length) {
		if (!this.IsInteger(length) || length < 0) {
			throw new $TypeError('Assertion failed: length must be an integer >= 0');
		}
		var len = length === 0 ? 0 : length;
		var C;
		var isArray = this.IsArray(originalArray);
		if (isArray) {
			C = this.Get(originalArray, 'constructor');
			// TODO: figure out how to make a cross-realm normal Array, a same-realm Array
			// if (this.IsConstructor(C)) {
			// 	if C is another realm's Array, C = undefined
			// 	Object.getPrototypeOf(Object.getPrototypeOf(Object.getPrototypeOf(Array))) === null ?
			// }
			if (this.Type(C) === 'Object' && hasSymbols && $Symbol.species) {
				C = this.Get(C, $Symbol.species);
				if (C === null) {
					C = void 0;
				}
			}
		}
		if (typeof C === 'undefined') {
			return $Array(len);
		}
		if (!this.IsConstructor(C)) {
			throw new $TypeError('C must be a constructor');
		}
		return new C(len); // this.Construct(C, len);
	},

	CreateDataProperty: function CreateDataProperty(O, P, V) {
		if (this.Type(O) !== 'Object') {
			throw new $TypeError('Assertion failed: Type(O) is not Object');
		}
		if (!this.IsPropertyKey(P)) {
			throw new $TypeError('Assertion failed: IsPropertyKey(P) is not true');
		}
		var oldDesc = $gOPD(O, P);
		var extensible = oldDesc || this.IsExtensible(O);
		var immutable = oldDesc && (!oldDesc.writable || !oldDesc.configurable);
		if (immutable || !extensible) {
			return false;
		}
		return DefineOwnProperty(this, O, P, {
			'[[Configurable]]': true,
			'[[Enumerable]]': true,
			'[[Value]]': V,
			'[[Writable]]': true
		});
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-createdatapropertyorthrow
	CreateDataPropertyOrThrow: function CreateDataPropertyOrThrow(O, P, V) {
		if (this.Type(O) !== 'Object') {
			throw new $TypeError('Assertion failed: Type(O) is not Object');
		}
		if (!this.IsPropertyKey(P)) {
			throw new $TypeError('Assertion failed: IsPropertyKey(P) is not true');
		}
		var success = this.CreateDataProperty(O, P, V);
		if (!success) {
			throw new $TypeError('unable to create data property');
		}
		return success;
	},

	// https://www.ecma-international.org/ecma-262/6.0/#sec-objectcreate
	ObjectCreate: function ObjectCreate(proto, internalSlotsList) {
		if (proto !== null && this.Type(proto) !== 'Object') {
			throw new $TypeError('Assertion failed: proto must be null or an object');
		}
		var slots = arguments.length < 2 ? [] : internalSlotsList;
		if (slots.length > 0) {
			throw new $SyntaxError('es-abstract does not yet support internal slots');
		}

		if (proto === null && !$ObjectCreate) {
			throw new $SyntaxError('native Object.create support is required to create null objects');
		}

		return $ObjectCreate(proto);
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-advancestringindex
	AdvanceStringIndex: function AdvanceStringIndex(S, index, unicode) {
		if (this.Type(S) !== 'String') {
			throw new $TypeError('S must be a String');
		}
		if (!this.IsInteger(index) || index < 0 || index > MAX_SAFE_INTEGER) {
			throw new $TypeError('Assertion failed: length must be an integer >= 0 and <= 2**53');
		}
		if (this.Type(unicode) !== 'Boolean') {
			throw new $TypeError('Assertion failed: unicode must be a Boolean');
		}
		if (!unicode) {
			return index + 1;
		}
		var length = S.length;
		if ((index + 1) >= length) {
			return index + 1;
		}

		var first = $charCodeAt(S, index);
		if (first < 0xD800 || first > 0xDBFF) {
			return index + 1;
		}

		var second = $charCodeAt(S, index + 1);
		if (second < 0xDC00 || second > 0xDFFF) {
			return index + 1;
		}

		return index + 2;
	},

	// https://www.ecma-international.org/ecma-262/6.0/#sec-createmethodproperty
	CreateMethodProperty: function CreateMethodProperty(O, P, V) {
		if (this.Type(O) !== 'Object') {
			throw new $TypeError('Assertion failed: Type(O) is not Object');
		}

		if (!this.IsPropertyKey(P)) {
			throw new $TypeError('Assertion failed: IsPropertyKey(P) is not true');
		}

		var newDesc = {
			'[[Configurable]]': true,
			'[[Enumerable]]': false,
			'[[Value]]': V,
			'[[Writable]]': true
		};
		return DefineOwnProperty(this, O, P, newDesc);
	},

	// https://www.ecma-international.org/ecma-262/6.0/#sec-definepropertyorthrow
	DefinePropertyOrThrow: function DefinePropertyOrThrow(O, P, desc) {
		if (this.Type(O) !== 'Object') {
			throw new $TypeError('Assertion failed: Type(O) is not Object');
		}

		if (!this.IsPropertyKey(P)) {
			throw new $TypeError('Assertion failed: IsPropertyKey(P) is not true');
		}

		var Desc = isPropertyDescriptor(this, desc) ? desc : this.ToPropertyDescriptor(desc);
		if (!isPropertyDescriptor(this, Desc)) {
			throw new $TypeError('Assertion failed: Desc is not a valid Property Descriptor');
		}

		return DefineOwnProperty(this, O, P, Desc);
	},

	// https://www.ecma-international.org/ecma-262/6.0/#sec-deletepropertyorthrow
	DeletePropertyOrThrow: function DeletePropertyOrThrow(O, P) {
		if (this.Type(O) !== 'Object') {
			throw new $TypeError('Assertion failed: Type(O) is not Object');
		}

		if (!this.IsPropertyKey(P)) {
			throw new $TypeError('Assertion failed: IsPropertyKey(P) is not true');
		}

		var success = delete O[P];
		if (!success) {
			throw new TypeError('Attempt to delete property failed.');
		}
		return success;
	},

	// https://www.ecma-international.org/ecma-262/6.0/#sec-enumerableownnames
	EnumerableOwnNames: function EnumerableOwnNames(O) {
		if (this.Type(O) !== 'Object') {
			throw new $TypeError('Assertion failed: Type(O) is not Object');
		}

		return keys(O);
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-properties-of-the-number-prototype-object
	thisNumberValue: function thisNumberValue(value) {
		if (this.Type(value) === 'Number') {
			return value;
		}

		return $NumberValueOf(value);
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-properties-of-the-boolean-prototype-object
	thisBooleanValue: function thisBooleanValue(value) {
		if (this.Type(value) === 'Boolean') {
			return value;
		}

		return $BooleanValueOf(value);
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-properties-of-the-string-prototype-object
	thisStringValue: function thisStringValue(value) {
		if (this.Type(value) === 'String') {
			return value;
		}

		return $StringValueOf(value);
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-properties-of-the-date-prototype-object
	thisTimeValue: function thisTimeValue(value) {
		return $DateValueOf(value);
	},

	// https://www.ecma-international.org/ecma-262/6.0/#sec-setintegritylevel
	SetIntegrityLevel: function SetIntegrityLevel(O, level) {
		if (this.Type(O) !== 'Object') {
			throw new $TypeError('Assertion failed: Type(O) is not Object');
		}
		if (level !== 'sealed' && level !== 'frozen') {
			throw new $TypeError('Assertion failed: `level` must be `"sealed"` or `"frozen"`');
		}
		if (!$preventExtensions) {
			throw new $SyntaxError('SetIntegrityLevel requires native `Object.preventExtensions` support');
		}
		var status = $preventExtensions(O);
		if (!status) {
			return false;
		}
		if (!$gOPN) {
			throw new $SyntaxError('SetIntegrityLevel requires native `Object.getOwnPropertyNames` support');
		}
		var theKeys = $gOPN(O);
		var ES = this;
		if (level === 'sealed') {
			forEach(theKeys, function (k) {
				ES.DefinePropertyOrThrow(O, k, { configurable: false });
			});
		} else if (level === 'frozen') {
			forEach(theKeys, function (k) {
				var currentDesc = $gOPD(O, k);
				if (typeof currentDesc !== 'undefined') {
					var desc;
					if (ES.IsAccessorDescriptor(ES.ToPropertyDescriptor(currentDesc))) {
						desc = { configurable: false };
					} else {
						desc = { configurable: false, writable: false };
					}
					ES.DefinePropertyOrThrow(O, k, desc);
				}
			});
		}
		return true;
	},

	// https://www.ecma-international.org/ecma-262/6.0/#sec-testintegritylevel
	TestIntegrityLevel: function TestIntegrityLevel(O, level) {
		if (this.Type(O) !== 'Object') {
			throw new $TypeError('Assertion failed: Type(O) is not Object');
		}
		if (level !== 'sealed' && level !== 'frozen') {
			throw new $TypeError('Assertion failed: `level` must be `"sealed"` or `"frozen"`');
		}
		var status = this.IsExtensible(O);
		if (status) {
			return false;
		}
		var theKeys = $gOPN(O);
		var ES = this;
		return theKeys.length === 0 || every(theKeys, function (k) {
			var currentDesc = $gOPD(O, k);
			if (typeof currentDesc !== 'undefined') {
				if (currentDesc.configurable) {
					return false;
				}
				if (level === 'frozen' && ES.IsDataDescriptor(ES.ToPropertyDescriptor(currentDesc)) && currentDesc.writable) {
					return false;
				}
			}
			return true;
		});
	},

	// https://www.ecma-international.org/ecma-262/6.0/#sec-ordinaryhasinstance
	OrdinaryHasInstance: function OrdinaryHasInstance(C, O) {
		if (this.IsCallable(C) === false) {
			return false;
		}
		if (this.Type(O) !== 'Object') {
			return false;
		}
		var P = this.Get(C, 'prototype');
		if (this.Type(P) !== 'Object') {
			throw new $TypeError('OrdinaryHasInstance called on an object with an invalid prototype property.');
		}
		return O instanceof C;
	},

	// https://www.ecma-international.org/ecma-262/6.0/#sec-ordinaryhasproperty
	OrdinaryHasProperty: function OrdinaryHasProperty(O, P) {
		if (this.Type(O) !== 'Object') {
			throw new $TypeError('Assertion failed: Type(O) is not Object');
		}
		if (!this.IsPropertyKey(P)) {
			throw new $TypeError('Assertion failed: P must be a Property Key');
		}
		return P in O;
	},

	// https://www.ecma-international.org/ecma-262/6.0/#sec-instanceofoperator
	InstanceofOperator: function InstanceofOperator(O, C) {
		if (this.Type(O) !== 'Object') {
			throw new $TypeError('Assertion failed: Type(O) is not Object');
		}
		var instOfHandler = hasSymbols && $Symbol.hasInstance ? this.GetMethod(C, $Symbol.hasInstance) : void 0;
		if (typeof instOfHandler !== 'undefined') {
			return this.ToBoolean(this.Call(instOfHandler, C, [O]));
		}
		if (!this.IsCallable(C)) {
			throw new $TypeError('`C` is not Callable');
		}
		return this.OrdinaryHasInstance(C, O);
	},

	// https://www.ecma-international.org/ecma-262/6.0/#sec-ispromise
	IsPromise: function IsPromise(x) {
		if (this.Type(x) !== 'Object') {
			return false;
		}
		if (!$PromiseThen) { // Promises are not supported
			return false;
		}
		try {
			$PromiseThen(x); // throws if not a promise
		} catch (e) {
			return false;
		}
		return true;
	},

	// https://www.ecma-international.org/ecma-262/6.0/#sec-abstract-equality-comparison
	'Abstract Equality Comparison': function AbstractEqualityComparison(x, y) {
		var xType = this.Type(x);
		var yType = this.Type(y);
		if (xType === yType) {
			return x === y; // ES6+ specified this shortcut anyways.
		}
		if (x == null && y == null) {
			return true;
		}
		if (xType === 'Number' && yType === 'String') {
			return this['Abstract Equality Comparison'](x, this.ToNumber(y));
		}
		if (xType === 'String' && yType === 'Number') {
			return this['Abstract Equality Comparison'](this.ToNumber(x), y);
		}
		if (xType === 'Boolean') {
			return this['Abstract Equality Comparison'](this.ToNumber(x), y);
		}
		if (yType === 'Boolean') {
			return this['Abstract Equality Comparison'](x, this.ToNumber(y));
		}
		if ((xType === 'String' || xType === 'Number' || xType === 'Symbol') && yType === 'Object') {
			return this['Abstract Equality Comparison'](x, this.ToPrimitive(y));
		}
		if (xType === 'Object' && (yType === 'String' || yType === 'Number' || yType === 'Symbol')) {
			return this['Abstract Equality Comparison'](this.ToPrimitive(x), y);
		}
		return false;
	},

	// eslint-disable-next-line max-lines-per-function, max-statements, id-length, max-params
	ValidateAndApplyPropertyDescriptor: function ValidateAndApplyPropertyDescriptor(O, P, extensible, Desc, current) {
		// this uses the ES2017+ logic, since it fixes a number of bugs in the ES2015 logic.
		var oType = this.Type(O);
		if (oType !== 'Undefined' && oType !== 'Object') {
			throw new $TypeError('Assertion failed: O must be undefined or an Object');
		}
		if (this.Type(extensible) !== 'Boolean') {
			throw new $TypeError('Assertion failed: extensible must be a Boolean');
		}
		if (!isPropertyDescriptor(this, Desc)) {
			throw new $TypeError('Assertion failed: Desc must be a Property Descriptor');
		}
		if (this.Type(current) !== 'Undefined' && !isPropertyDescriptor(this, current)) {
			throw new $TypeError('Assertion failed: current must be a Property Descriptor, or undefined');
		}
		if (oType !== 'Undefined' && !this.IsPropertyKey(P)) {
			throw new $TypeError('Assertion failed: if O is not undefined, P must be a Property Key');
		}
		if (this.Type(current) === 'Undefined') {
			if (!extensible) {
				return false;
			}
			if (this.IsGenericDescriptor(Desc) || this.IsDataDescriptor(Desc)) {
				if (oType !== 'Undefined') {
					DefineOwnProperty(this, O, P, {
						'[[Configurable]]': Desc['[[Configurable]]'],
						'[[Enumerable]]': Desc['[[Enumerable]]'],
						'[[Value]]': Desc['[[Value]]'],
						'[[Writable]]': Desc['[[Writable]]']
					});
				}
			} else {
				if (!this.IsAccessorDescriptor(Desc)) {
					throw new $TypeError('Assertion failed: Desc is not an accessor descriptor');
				}
				if (oType !== 'Undefined') {
					return DefineOwnProperty(this, O, P, Desc);
				}
			}
			return true;
		}
		if (this.IsGenericDescriptor(Desc) && !('[[Configurable]]' in Desc) && !('[[Enumerable]]' in Desc)) {
			return true;
		}
		if (isSamePropertyDescriptor(this, Desc, current)) {
			return true; // removed by ES2017, but should still be correct
		}
		// "if every field in Desc is absent, return true" can't really match the assertion that it's a Property Descriptor
		if (!current['[[Configurable]]']) {
			if (Desc['[[Configurable]]']) {
				return false;
			}
			if ('[[Enumerable]]' in Desc && !Desc['[[Enumerable]]'] === !!current['[[Enumerable]]']) {
				return false;
			}
		}
		if (this.IsGenericDescriptor(Desc)) {
			// no further validation is required.
		} else if (this.IsDataDescriptor(current) !== this.IsDataDescriptor(Desc)) {
			if (!current['[[Configurable]]']) {
				return false;
			}
			if (this.IsDataDescriptor(current)) {
				if (oType !== 'Undefined') {
					DefineOwnProperty(this, O, P, {
						'[[Configurable]]': current['[[Configurable]]'],
						'[[Enumerable]]': current['[[Enumerable]]'],
						'[[Get]]': undefined
					});
				}
			} else if (oType !== 'Undefined') {
				DefineOwnProperty(this, O, P, {
					'[[Configurable]]': current['[[Configurable]]'],
					'[[Enumerable]]': current['[[Enumerable]]'],
					'[[Value]]': undefined
				});
			}
		} else if (this.IsDataDescriptor(current) && this.IsDataDescriptor(Desc)) {
			if (!current['[[Configurable]]'] && !current['[[Writable]]']) {
				if ('[[Writable]]' in Desc && Desc['[[Writable]]']) {
					return false;
				}
				if ('[[Value]]' in Desc && !this.SameValue(Desc['[[Value]]'], current['[[Value]]'])) {
					return false;
				}
				return true;
			}
		} else if (this.IsAccessorDescriptor(current) && this.IsAccessorDescriptor(Desc)) {
			if (!current['[[Configurable]]']) {
				if ('[[Set]]' in Desc && !this.SameValue(Desc['[[Set]]'], current['[[Set]]'])) {
					return false;
				}
				if ('[[Get]]' in Desc && !this.SameValue(Desc['[[Get]]'], current['[[Get]]'])) {
					return false;
				}
				return true;
			}
		} else {
			throw new $TypeError('Assertion failed: current and Desc are not both data, both accessors, or one accessor and one data.');
		}
		if (oType !== 'Undefined') {
			return DefineOwnProperty(this, O, P, Desc);
		}
		return true;
	},

	// https://www.ecma-international.org/ecma-262/6.0/#sec-ordinarydefineownproperty
	OrdinaryDefineOwnProperty: function OrdinaryDefineOwnProperty(O, P, Desc) {
		if (this.Type(O) !== 'Object') {
			throw new $TypeError('Assertion failed: O must be an Object');
		}
		if (!this.IsPropertyKey(P)) {
			throw new $TypeError('Assertion failed: P must be a Property Key');
		}
		if (!isPropertyDescriptor(this, Desc)) {
			throw new $TypeError('Assertion failed: Desc must be a Property Descriptor');
		}
		var desc = $gOPD(O, P);
		var current = desc && this.ToPropertyDescriptor(desc);
		var extensible = this.IsExtensible(O);
		return this.ValidateAndApplyPropertyDescriptor(O, P, extensible, Desc, current);
	},

	// https://www.ecma-international.org/ecma-262/6.0/#sec-ordinarygetownproperty
	OrdinaryGetOwnProperty: function OrdinaryGetOwnProperty(O, P) {
		if (this.Type(O) !== 'Object') {
			throw new $TypeError('Assertion failed: O must be an Object');
		}
		if (!this.IsPropertyKey(P)) {
			throw new $TypeError('Assertion failed: P must be a Property Key');
		}
		if (!has(O, P)) {
			return void 0;
		}
		if (!$gOPD) {
			// ES3 fallback
			var arrayLength = this.IsArray(O) && P === 'length';
			var regexLastIndex = this.IsRegExp(O) && P === 'lastIndex';
			return {
				'[[Configurable]]': !(arrayLength || regexLastIndex),
				'[[Enumerable]]': $isEnumerable(O, P),
				'[[Value]]': O[P],
				'[[Writable]]': true
			};
		}
		return this.ToPropertyDescriptor($gOPD(O, P));
	},

	// https://www.ecma-international.org/ecma-262/6.0/#sec-arraycreate
	ArrayCreate: function ArrayCreate(length) {
		if (!this.IsInteger(length) || length < 0) {
			throw new $TypeError('Assertion failed: `length` must be an integer Number >= 0');
		}
		if (length > MAX_ARRAY_LENGTH) {
			throw new $RangeError('length is greater than (2**32 - 1)');
		}
		var proto = arguments.length > 1 ? arguments[1] : $ArrayPrototype;
		var A = []; // steps 5 - 7, and 9
		if (proto !== $ArrayPrototype) { // step 8
			if (!$setProto) {
				throw new $SyntaxError('ArrayCreate: a `proto` argument that is not `Array.prototype` is not supported in an environment that does not support setting the [[Prototype]]');
			}
			$setProto(A, proto);
		}
		if (length !== 0) { // bypasses the need for step 2
			A.length = length;
		}
		/* step 10, the above as a shortcut for the below
		this.OrdinaryDefineOwnProperty(A, 'length', {
			'[[Configurable]]': false,
			'[[Enumerable]]': false,
			'[[Value]]': length,
			'[[Writable]]': true
		});
		*/
		return A;
	},

	// eslint-disable-next-line max-statements, max-lines-per-function
	ArraySetLength: function ArraySetLength(A, Desc) {
		if (!this.IsArray(A)) {
			throw new $TypeError('Assertion failed: A must be an Array');
		}
		if (!isPropertyDescriptor(this, Desc)) {
			throw new $TypeError('Assertion failed: Desc must be a Property Descriptor');
		}
		if (!('[[Value]]' in Desc)) {
			return this.OrdinaryDefineOwnProperty(A, 'length', Desc);
		}
		var newLenDesc = assign({}, Desc);
		var newLen = this.ToUint32(Desc['[[Value]]']);
		var numberLen = this.ToNumber(Desc['[[Value]]']);
		if (newLen !== numberLen) {
			throw new $RangeError('Invalid array length');
		}
		newLenDesc['[[Value]]'] = newLen;
		var oldLenDesc = this.OrdinaryGetOwnProperty(A, 'length');
		if (!this.IsDataDescriptor(oldLenDesc)) {
			throw new $TypeError('Assertion failed: an array had a non-data descriptor on `length`');
		}
		var oldLen = oldLenDesc['[[Value]]'];
		if (newLen >= oldLen) {
			return this.OrdinaryDefineOwnProperty(A, 'length', newLenDesc);
		}
		if (!oldLenDesc['[[Writable]]']) {
			return false;
		}
		var newWritable;
		if (!('[[Writable]]' in newLenDesc) || newLenDesc['[[Writable]]']) {
			newWritable = true;
		} else {
			newWritable = false;
			newLenDesc['[[Writable]]'] = true;
		}
		var succeeded = this.OrdinaryDefineOwnProperty(A, 'length', newLenDesc);
		if (!succeeded) {
			return false;
		}
		while (newLen < oldLen) {
			oldLen -= 1;
			var deleteSucceeded = delete A[this.ToString(oldLen)];
			if (!deleteSucceeded) {
				newLenDesc['[[Value]]'] = oldLen + 1;
				if (!newWritable) {
					newLenDesc['[[Writable]]'] = false;
					this.OrdinaryDefineOwnProperty(A, 'length', newLenDesc);
					return false;
				}
			}
		}
		if (!newWritable) {
			return this.OrdinaryDefineOwnProperty(A, 'length', { '[[Writable]]': false });
		}
		return true;
	},

	// https://www.ecma-international.org/ecma-262/6.0/#sec-createhtml
	CreateHTML: function CreateHTML(string, tag, attribute, value) {
		if (this.Type(tag) !== 'String' || this.Type(attribute) !== 'String') {
			throw new $TypeError('Assertion failed: `tag` and `attribute` must be strings');
		}
		var str = this.RequireObjectCoercible(string);
		var S = this.ToString(str);
		var p1 = '<' + tag;
		if (attribute !== '') {
			var V = this.ToString(value);
			var escapedV = $replace(V, /\x22/g, '&quot;');
			p1 += '\x20' + attribute + '\x3D\x22' + escapedV + '\x22';
		}
		return p1 + '>' + S + '</' + tag + '>';
	},

	// https://www.ecma-international.org/ecma-262/6.0/#sec-getownpropertykeys
	GetOwnPropertyKeys: function GetOwnPropertyKeys(O, Type) {
		if (this.Type(O) !== 'Object') {
			throw new $TypeError('Assertion failed: Type(O) is not Object');
		}
		if (Type === 'Symbol') {
			return hasSymbols && $gOPS ? $gOPS(O) : [];
		}
		if (Type === 'String') {
			if (!$gOPN) {
				return keys(O);
			}
			return $gOPN(O);
		}
		throw new $TypeError('Assertion failed: `Type` must be `"String"` or `"Symbol"`');
	},

	// https://www.ecma-international.org/ecma-262/6.0/#sec-symboldescriptivestring
	SymbolDescriptiveString: function SymbolDescriptiveString(sym) {
		if (this.Type(sym) !== 'Symbol') {
			throw new $TypeError('Assertion failed: `sym` must be a Symbol');
		}
		return $SymbolToString(sym);
	},

	// https://www.ecma-international.org/ecma-262/6.0/#sec-getsubstitution
	// eslint-disable-next-line max-statements, max-params, max-lines-per-function
	GetSubstitution: function GetSubstitution(matched, str, position, captures, replacement) {
		if (this.Type(matched) !== 'String') {
			throw new $TypeError('Assertion failed: `matched` must be a String');
		}
		var matchLength = matched.length;

		if (this.Type(str) !== 'String') {
			throw new $TypeError('Assertion failed: `str` must be a String');
		}
		var stringLength = str.length;

		if (!this.IsInteger(position) || position < 0 || position > stringLength) {
			throw new $TypeError('Assertion failed: `position` must be a nonnegative integer, and less than or equal to the length of `string`, got ' + inspect(position));
		}

		var ES = this;
		var isStringOrHole = function (capture, index, arr) { return ES.Type(capture) === 'String' || !(index in arr); };
		if (!this.IsArray(captures) || !every(captures, isStringOrHole)) {
			throw new $TypeError('Assertion failed: `captures` must be a List of Strings, got ' + inspect(captures));
		}

		if (this.Type(replacement) !== 'String') {
			throw new $TypeError('Assertion failed: `replacement` must be a String');
		}

		var tailPos = position + matchLength;
		var m = captures.length;

		var result = '';
		for (var i = 0; i < replacement.length; i += 1) {
			// if this is a $, and it's not the end of the replacement
			var current = replacement[i];
			var isLast = (i + 1) >= replacement.length;
			var nextIsLast = (i + 2) >= replacement.length;
			if (current === '$' && !isLast) {
				var next = replacement[i + 1];
				if (next === '$') {
					result += '$';
					i += 1;
				} else if (next === '&') {
					result += matched;
					i += 1;
				} else if (next === '`') {
					result += position === 0 ? '' : strSlice(str, 0, position - 1);
					i += 1;
				} else if (next === "'") {
					result += tailPos >= stringLength ? '' : strSlice(str, tailPos);
					i += 1;
				} else {
					var nextNext = nextIsLast ? null : replacement[i + 2];
					if (isDigit(next) && next !== '0' && (nextIsLast || !isDigit(nextNext))) {
						// $1 through $9, and not followed by a digit
						var n = parseInteger(next, 10);
						// if (n > m, impl-defined)
						result += (n <= m && this.Type(captures[n - 1]) === 'Undefined') ? '' : captures[n - 1];
						i += 1;
					} else if (isDigit(next) && (nextIsLast || isDigit(nextNext))) {
						// $00 through $99
						var nn = next + nextNext;
						var nnI = parseInteger(nn, 10) - 1;
						// if nn === '00' or nn > m, impl-defined
						result += (nn <= m && this.Type(captures[nnI]) === 'Undefined') ? '' : captures[nnI];
						i += 2;
					} else {
						result += '$';
					}
				}
			} else {
				// the final $, or else not a $
				result += replacement[i];
			}
		}
		return result;
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-todatestring
	ToDateString: function ToDateString(tv) {
		if (this.Type(tv) !== 'Number') {
			throw new $TypeError('Assertion failed: `tv` must be a Number');
		}
		if ($isNaN(tv)) {
			return 'Invalid Date';
		}
		return $Date(tv);
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-createlistfromarraylike
	CreateListFromArrayLike: function CreateListFromArrayLike(obj) {
		var elementTypes = arguments.length > 1
			? arguments[1]
			: ['Undefined', 'Null', 'Boolean', 'String', 'Symbol', 'Number', 'Object'];

		if (this.Type(obj) !== 'Object') {
			throw new $TypeError('Assertion failed: `obj` must be an Object');
		}
		if (!this.IsArray(elementTypes)) {
			throw new $TypeError('Assertion failed: `elementTypes`, if provided, must be an array');
		}
		var len = this.ToLength(this.Get(obj, 'length'));
		var list = [];
		var index = 0;
		while (index < len) {
			var indexName = this.ToString(index);
			var next = this.Get(obj, indexName);
			var nextType = this.Type(next);
			if ($indexOf(elementTypes, nextType) < 0) {
				throw new $TypeError('item type ' + nextType + ' is not a valid elementType');
			}
			$push(list, next);
			index += 1;
		}
		return list;
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-getprototypefromconstructor
	GetPrototypeFromConstructor: function GetPrototypeFromConstructor(constructor, intrinsicDefaultProto) {
		var intrinsic = GetIntrinsic(intrinsicDefaultProto); // throws if not a valid intrinsic
		if (!this.IsConstructor(constructor)) {
			throw new $TypeError('Assertion failed: `constructor` must be a constructor');
		}
		var proto = this.Get(constructor, 'prototype');
		if (this.Type(proto) !== 'Object') {
			if (!(constructor instanceof $Function)) {
				// ignore other realms, for now
				throw new $TypeError('cross-realm constructors not currently supported');
			}
			proto = intrinsic;
		}
		return proto;
	},

	// https://ecma-international.org/ecma-262/6.0/#sec-setfunctionname
	SetFunctionName: function SetFunctionName(F, name) {
		if (typeof F !== 'function') {
			throw new $TypeError('Assertion failed: `F` must be a function');
		}
		if (!this.IsExtensible(F) || has(F, 'name')) {
			throw new $TypeError('Assertion failed: `F` must be extensible, and must not have a `name` own property');
		}
		var nameType = this.Type(name);
		if (nameType !== 'Symbol' && nameType !== 'String') {
			throw new $TypeError('Assertion failed: `name` must be a Symbol or a String');
		}
		if (nameType === 'Symbol') {
			var description = getSymbolDescription(name);
			// eslint-disable-next-line no-param-reassign
			name = typeof description === 'undefined' ? '' : '[' + description + ']';
		}
		if (arguments.length > 2) {
			var prefix = arguments[2];
			// eslint-disable-next-line no-param-reassign
			name = prefix + ' ' + name;
		}
		return this.DefinePropertyOrThrow(F, 'name', {
			'[[Value]]': name,
			'[[Writable]]': false,
			'[[Enumerable]]': false,
			'[[Configurable]]': true
		});
	}
});

delete ES6.CheckObjectCoercible; // renamed in ES6 to RequireObjectCoercible

module.exports = ES6;