/*!
  * https://github.com/paulmillr/es6-shim
  * @license es6-shim Copyright 2013-2014 by Paul Miller (http://paulmillr.com)
  *   and contributors,  MIT License
  * es6-shim: v0.20.2
  * see https://github.com/paulmillr/es6-shim/blob/master/LICENSE
  * Details and documentation:
  * https://github.com/paulmillr/es6-shim/
  */

// UMD (Universal Module Definition)
// see https://github.com/umdjs/umd/blob/master/returnExports.js
(function (root, factory) {
  if (typeof define === 'function' && define.amd) {
    // AMD. Register as an anonymous module.
    define(factory);
  } else if (typeof exports === 'object') {
    // Node. Does not work with strict CommonJS, but
    // only CommonJS-like enviroments that support module.exports,
    // like Node.
    module.exports = factory();
  } else {
    // Browser globals (root is window)
    root.returnExports = factory();
  }
}(this, function () {
  'use strict';

  var isCallableWithoutNew = function (func) {
    try { func(); }
    catch (e) { return false; }
    return true;
  };

  var supportsSubclassing = function (C, f) {
    /* jshint proto:true */
    try {
      var Sub = function () { C.apply(this, arguments); };
      if (!Sub.__proto__) { return false; /* skip test on IE < 11 */ }
      Object.setPrototypeOf(Sub, C);
      Sub.prototype = Object.create(C.prototype, {
        constructor: { value: C }
      });
      return f(Sub);
    } catch (e) {
      return false;
    }
  };

  var arePropertyDescriptorsSupported = function () {
    try {
      Object.defineProperty({}, 'x', {});
      return true;
    } catch (e) { /* this is IE 8. */
      return false;
    }
  };

  var startsWithRejectsRegex = function () {
    var rejectsRegex = false;
    if (String.prototype.startsWith) {
      try {
        '/a/'.startsWith(/a/);
      } catch (e) { /* this is spec compliant */
        rejectsRegex = true;
      }
    }
    return rejectsRegex;
  };

  /*jshint evil: true */
  var getGlobal = new Function('return this;');
  /*jshint evil: false */

  var globals = getGlobal();
  var global_isFinite = globals.isFinite;
  var supportsDescriptors = !!Object.defineProperty && arePropertyDescriptorsSupported();
  var startsWithIsCompliant = startsWithRejectsRegex();
  var _slice = Array.prototype.slice;
  var _indexOf = String.prototype.indexOf;
  var _toString = Object.prototype.toString;
  var _hasOwnProperty = Object.prototype.hasOwnProperty;
  var ArrayIterator; // make our implementation private

  var defineProperty = function (object, name, value, force) {
    if (!force && name in object) { return; }
    if (supportsDescriptors) {
      Object.defineProperty(object, name, {
        configurable: true,
        enumerable: false,
        writable: true,
        value: value
      });
    } else {
      object[name] = value;
    }
  };

  // Define configurable, writable and non-enumerable props
  // if they don’t exist.
  var defineProperties = function (object, map) {
    Object.keys(map).forEach(function (name) {
      var method = map[name];
      defineProperty(object, name, method, false);
    });
  };

  // Simple shim for Object.create on ES3 browsers
  // (unlike real shim, no attempt to support `prototype === null`)
  var create = Object.create || function (prototype, properties) {
    function Type() {}
    Type.prototype = prototype;
    var object = new Type();
    if (typeof properties !== 'undefined') {
      defineProperties(object, properties);
    }
    return object;
  };

  // This is a private name in the es6 spec, equal to '[Symbol.iterator]'
  // we're going to use an arbitrary _-prefixed name to make our shims
  // work properly with each other, even though we don't have full Iterator
  // support.  That is, `Array.from(map.keys())` will work, but we don't
  // pretend to export a "real" Iterator interface.
  var $iterator$ = (typeof Symbol === 'function' && Symbol.iterator) ||
    '_es6shim_iterator_';
  // Firefox ships a partial implementation using the name @@iterator.
  // https://bugzilla.mozilla.org/show_bug.cgi?id=907077#c14
  // So use that name if we detect it.
  if (globals.Set && typeof new globals.Set()['@@iterator'] === 'function') {
    $iterator$ = '@@iterator';
  }
  var addIterator = function (prototype, impl) {
    if (!impl) { impl = function iterator() { return this; }; }
    var o = {};
    o[$iterator$] = impl;
    defineProperties(prototype, o);
    /* jshint notypeof: true */
    if (!prototype[$iterator$] && typeof $iterator$ === 'symbol') {
      // implementations are buggy when $iterator$ is a Symbol
      prototype[$iterator$] = impl;
    }
  };

  // taken directly from https://github.com/ljharb/is-arguments/blob/master/index.js
  // can be replaced with require('is-arguments') if we ever use a build process instead
  var isArguments = function isArguments(value) {
    var str = _toString.call(value);
    var result = str === '[object Arguments]';
    if (!result) {
      result = str !== '[object Array]' &&
        value !== null &&
        typeof value === 'object' &&
        typeof value.length === 'number' &&
        value.length >= 0 &&
        _toString.call(value.callee) === '[object Function]';
    }
    return result;
  };

  var emulateES6construct = function (o) {
    if (!ES.TypeIsObject(o)) { throw new TypeError('bad object'); }
    // es5 approximation to es6 subclass semantics: in es6, 'new Foo'
    // would invoke Foo.@@create to allocation/initialize the new object.
    // In es5 we just get the plain object.  So if we detect an
    // uninitialized object, invoke o.constructor.@@create
    if (!o._es6construct) {
      if (o.constructor && ES.IsCallable(o.constructor['@@create'])) {
        o = o.constructor['@@create'](o);
      }
      defineProperties(o, { _es6construct: true });
    }
    return o;
  };

  var ES = {
    CheckObjectCoercible: function (x, optMessage) {
      /* jshint eqnull:true */
      if (x == null) {
        throw new TypeError(optMessage || 'Cannot call method on ' + x);
      }
      return x;
    },

    TypeIsObject: function (x) {
      /* jshint eqnull:true */
      // this is expensive when it returns false; use this function
      // when you expect it to return true in the common case.
      return x != null && Object(x) === x;
    },

    ToObject: function (o, optMessage) {
      return Object(ES.CheckObjectCoercible(o, optMessage));
    },

    IsCallable: function (x) {
      return typeof x === 'function' &&
        // some versions of IE say that typeof /abc/ === 'function'
        _toString.call(x) === '[object Function]';
    },

    ToInt32: function (x) {
      return x >> 0;
    },

    ToUint32: function (x) {
      return x >>> 0;
    },

    ToInteger: function (value) {
      var number = +value;
      if (Number.isNaN(number)) { return 0; }
      if (number === 0 || !Number.isFinite(number)) { return number; }
      return (number > 0 ? 1 : -1) * Math.floor(Math.abs(number));
    },

    ToLength: function (value) {
      var len = ES.ToInteger(value);
      if (len <= 0) { return 0; } // includes converting -0 to +0
      if (len > Number.MAX_SAFE_INTEGER) { return Number.MAX_SAFE_INTEGER; }
      return len;
    },

    SameValue: function (a, b) {
      if (a === b) {
        // 0 === -0, but they are not identical.
        if (a === 0) { return 1 / a === 1 / b; }
        return true;
      }
      return Number.isNaN(a) && Number.isNaN(b);
    },

    SameValueZero: function (a, b) {
      // same as SameValue except for SameValueZero(+0, -0) == true
      return (a === b) || (Number.isNaN(a) && Number.isNaN(b));
    },

    IsIterable: function (o) {
      return ES.TypeIsObject(o) &&
        (typeof o[$iterator$] !== 'undefined' || isArguments(o));
    },

    GetIterator: function (o) {
      if (isArguments(o)) {
        // special case support for `arguments`
        return new ArrayIterator(o, 'value');
      }
      var it = o[$iterator$]();
      if (!ES.TypeIsObject(it)) {
        throw new TypeError('bad iterator');
      }
      return it;
    },

    IteratorNext: function (it) {
      var result = arguments.length > 1 ? it.next(arguments[1]) : it.next();
      if (!ES.TypeIsObject(result)) {
        throw new TypeError('bad iterator');
      }
      return result;
    },

    Construct: function (C, args) {
      // CreateFromConstructor
      var obj;
      if (ES.IsCallable(C['@@create'])) {
        obj = C['@@create']();
      } else {
        // OrdinaryCreateFromConstructor
        obj = create(C.prototype || null);
      }
      // Mark that we've used the es6 construct path
      // (see emulateES6construct)
      defineProperties(obj, { _es6construct: true });
      // Call the constructor.
      var result = C.apply(obj, args);
      return ES.TypeIsObject(result) ? result : obj;
    }
  };

  var numberConversion = (function () {
    // from https://github.com/inexorabletash/polyfill/blob/master/typedarray.js#L176-L266
    // with permission and license, per https://twitter.com/inexorabletash/status/372206509540659200

    function roundToEven(n) {
      var w = Math.floor(n), f = n - w;
      if (f < 0.5) {
        return w;
      }
      if (f > 0.5) {
        return w + 1;
      }
      return w % 2 ? w + 1 : w;
    }

    function packIEEE754(v, ebits, fbits) {
      var bias = (1 << (ebits - 1)) - 1,
        s, e, f, ln,
        i, bits, str, bytes;

      // Compute sign, exponent, fraction
      if (v !== v) {
        // NaN
        // http://dev.w3.org/2006/webapi/WebIDL/#es-type-mapping
        e = (1 << ebits) - 1;
        f = Math.pow(2, fbits - 1);
        s = 0;
      } else if (v === Infinity || v === -Infinity) {
        e = (1 << ebits) - 1;
        f = 0;
        s = (v < 0) ? 1 : 0;
      } else if (v === 0) {
        e = 0;
        f = 0;
        s = (1 / v === -Infinity) ? 1 : 0;
      } else {
        s = v < 0;
        v = Math.abs(v);

        if (v >= Math.pow(2, 1 - bias)) {
          e = Math.min(Math.floor(Math.log(v) / Math.LN2), 1023);
          f = roundToEven(v / Math.pow(2, e) * Math.pow(2, fbits));
          if (f / Math.pow(2, fbits) >= 2) {
            e = e + 1;
            f = 1;
          }
          if (e > bias) {
            // Overflow
            e = (1 << ebits) - 1;
            f = 0;
          } else {
            // Normal
            e = e + bias;
            f = f - Math.pow(2, fbits);
          }
        } else {
          // Subnormal
          e = 0;
          f = roundToEven(v / Math.pow(2, 1 - bias - fbits));
        }
      }

      // Pack sign, exponent, fraction
      bits = [];
      for (i = fbits; i; i -= 1) {
        bits.push(f % 2 ? 1 : 0);
        f = Math.floor(f / 2);
      }
      for (i = ebits; i; i -= 1) {
        bits.push(e % 2 ? 1 : 0);
        e = Math.floor(e / 2);
      }
      bits.push(s ? 1 : 0);
      bits.reverse();
      str = bits.join('');

      // Bits to bytes
      bytes = [];
      while (str.length) {
        bytes.push(parseInt(str.slice(0, 8), 2));
        str = str.slice(8);
      }
      return bytes;
    }

    function unpackIEEE754(bytes, ebits, fbits) {
      // Bytes to bits
      var bits = [], i, j, b, str,
          bias, s, e, f;

      for (i = bytes.length; i; i -= 1) {
        b = bytes[i - 1];
        for (j = 8; j; j -= 1) {
          bits.push(b % 2 ? 1 : 0);
          b = b >> 1;
        }
      }
      bits.reverse();
      str = bits.join('');

      // Unpack sign, exponent, fraction
      bias = (1 << (ebits - 1)) - 1;
      s = parseInt(str.slice(0, 1), 2) ? -1 : 1;
      e = parseInt(str.slice(1, 1 + ebits), 2);
      f = parseInt(str.slice(1 + ebits), 2);

      // Produce number
      if (e === (1 << ebits) - 1) {
        return f !== 0 ? NaN : s * Infinity;
      } else if (e > 0) {
        // Normalized
        return s * Math.pow(2, e - bias) * (1 + f / Math.pow(2, fbits));
      } else if (f !== 0) {
        // Denormalized
        return s * Math.pow(2, -(bias - 1)) * (f / Math.pow(2, fbits));
      } else {
        return s < 0 ? -0 : 0;
      }
    }

    function unpackFloat64(b) { return unpackIEEE754(b, 11, 52); }
    function packFloat64(v) { return packIEEE754(v, 11, 52); }
    function unpackFloat32(b) { return unpackIEEE754(b, 8, 23); }
    function packFloat32(v) { return packIEEE754(v, 8, 23); }

    var conversions = {
      toFloat32: function (num) { return unpackFloat32(packFloat32(num)); }
    };
    if (typeof Float32Array !== 'undefined') {
      var float32array = new Float32Array(1);
      conversions.toFloat32 = function (num) {
        float32array[0] = num;
        return float32array[0];
      };
    }
    return conversions;
  }());

  defineProperties(String, {
    fromCodePoint: function (_) { // length = 1
      var points = _slice.call(arguments, 0, arguments.length);
      var result = [];
      var next;
      for (var i = 0, length = points.length; i < length; i++) {
        next = Number(points[i]);
        if (!ES.SameValue(next, ES.ToInteger(next)) ||
            next < 0 || next > 0x10FFFF) {
          throw new RangeError('Invalid code point ' + next);
        }

        if (next < 0x10000) {
          result.push(String.fromCharCode(next));
        } else {
          next -= 0x10000;
          result.push(String.fromCharCode((next >> 10) + 0xD800));
          result.push(String.fromCharCode((next % 0x400) + 0xDC00));
        }
      }
      return result.join('');
    },

    raw: function (callSite) { // raw.length===1
      var substitutions = _slice.call(arguments, 1, arguments.length);
      var cooked = ES.ToObject(callSite, 'bad callSite');
      var rawValue = cooked.raw;
      var raw = ES.ToObject(rawValue, 'bad raw value');
      var len = Object.keys(raw).length;
      var literalsegments = ES.ToLength(len);
      if (literalsegments === 0) {
        return '';
      }

      var stringElements = [];
      var nextIndex = 0;
      var nextKey, next, nextSeg, nextSub;
      while (nextIndex < literalsegments) {
        nextKey = String(nextIndex);
        next = raw[nextKey];
        nextSeg = String(next);
        stringElements.push(nextSeg);
        if (nextIndex + 1 >= literalsegments) {
          break;
        }
        next = substitutions[nextKey];
        if (typeof next === 'undefined') {
          break;
        }
        nextSub = String(next);
        stringElements.push(nextSub);
        nextIndex++;
      }
      return stringElements.join('');
    }
  });

  // Firefox 31 reports this function's length as 0
  // https://bugzilla.mozilla.org/show_bug.cgi?id=1062484
  if (String.fromCodePoint.length !== 1) {
    var originalFromCodePoint = String.fromCodePoint;
    defineProperty(String, 'fromCodePoint', function (_) { return originalFromCodePoint.apply(this, arguments); }, true);
  }

  var StringShims = {
    // Fast repeat, uses the `Exponentiation by squaring` algorithm.
    // Perf: http://jsperf.com/string-repeat2/2
    repeat: (function () {
      var repeat = function (s, times) {
        if (times < 1) { return ''; }
        if (times % 2) { return repeat(s, times - 1) + s; }
        var half = repeat(s, times / 2);
        return half + half;
      };

      return function (times) {
        var thisStr = String(ES.CheckObjectCoercible(this));
        times = ES.ToInteger(times);
        if (times < 0 || times === Infinity) {
          throw new RangeError('Invalid String#repeat value');
        }
        return repeat(thisStr, times);
      };
    })(),

    startsWith: function (searchStr) {
      var thisStr = String(ES.CheckObjectCoercible(this));
      if (_toString.call(searchStr) === '[object RegExp]') {
        throw new TypeError('Cannot call method "startsWith" with a regex');
      }
      searchStr = String(searchStr);
      var startArg = arguments.length > 1 ? arguments[1] : void 0;
      var start = Math.max(ES.ToInteger(startArg), 0);
      return thisStr.slice(start, start + searchStr.length) === searchStr;
    },

    endsWith: function (searchStr) {
      var thisStr = String(ES.CheckObjectCoercible(this));
      if (_toString.call(searchStr) === '[object RegExp]') {
        throw new TypeError('Cannot call method "endsWith" with a regex');
      }
      searchStr = String(searchStr);
      var thisLen = thisStr.length;
      var posArg = arguments.length > 1 ? arguments[1] : void 0;
      var pos = typeof posArg === 'undefined' ? thisLen : ES.ToInteger(posArg);
      var end = Math.min(Math.max(pos, 0), thisLen);
      return thisStr.slice(end - searchStr.length, end) === searchStr;
    },

    contains: function (searchString) {
      var position = arguments.length > 1 ? arguments[1] : void 0;
      // Somehow this trick makes method 100% compat with the spec.
      return _indexOf.call(this, searchString, position) !== -1;
    },

    codePointAt: function (pos) {
      var thisStr = String(ES.CheckObjectCoercible(this));
      var position = ES.ToInteger(pos);
      var length = thisStr.length;
      if (position < 0 || position >= length) { return; }
      var first = thisStr.charCodeAt(position);
      var isEnd = (position + 1 === length);
      if (first < 0xD800 || first > 0xDBFF || isEnd) { return first; }
      var second = thisStr.charCodeAt(position + 1);
      if (second < 0xDC00 || second > 0xDFFF) { return first; }
      return ((first - 0xD800) * 1024) + (second - 0xDC00) + 0x10000;
    }
  };
  defineProperties(String.prototype, StringShims);

  var hasStringTrimBug = '\u0085'.trim().length !== 1;
  if (hasStringTrimBug) {
    var originalStringTrim = String.prototype.trim;
    delete String.prototype.trim;
    // whitespace from: http://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 trimRegexp = new RegExp('(^[' + ws + ']+)|([' + ws + ']+$)', 'g');
    defineProperties(String.prototype, {
      trim: function () {
        if (typeof this === 'undefined' || this === null) {
          throw new TypeError("can't convert " + this + ' to object');
        }
        return String(this).replace(trimRegexp, '');
      }
    });
  }

  // see https://people.mozilla.org/~jorendorff/es6-draft.html#sec-string.prototype-@@iterator
  var StringIterator = function (s) {
    this._s = String(ES.CheckObjectCoercible(s));
    this._i = 0;
  };
  StringIterator.prototype.next = function () {
    var s = this._s, i = this._i;
    if (typeof s === 'undefined' || i >= s.length) {
      this._s = void 0;
      return { value: void 0, done: true };
    }
    var first = s.charCodeAt(i), second, len;
    if (first < 0xD800 || first > 0xDBFF || (i + 1) == s.length) {
      len = 1;
    } else {
      second = s.charCodeAt(i + 1);
      len = (second < 0xDC00 || second > 0xDFFF) ? 1 : 2;
    }
    this._i = i + len;
    return { value: s.substr(i, len), done: false };
  };
  addIterator(StringIterator.prototype);
  addIterator(String.prototype, function () {
    return new StringIterator(this);
  });

  if (!startsWithIsCompliant) {
    // Firefox has a noncompliant startsWith implementation
    String.prototype.startsWith = StringShims.startsWith;
    String.prototype.endsWith = StringShims.endsWith;
  }

  var ArrayShims = {
    from: function (iterable) {
      var mapFn = arguments.length > 1 ? arguments[1] : void 0;

      var list = ES.ToObject(iterable, 'bad iterable');
      if (typeof mapFn !== 'undefined' && !ES.IsCallable(mapFn)) {
        throw new TypeError('Array.from: when provided, the second argument must be a function');
      }

      var hasThisArg = arguments.length > 2;
      var thisArg = hasThisArg ? arguments[2] : void 0;

      var usingIterator = ES.IsIterable(list);
      // does the spec really mean that Arrays should use ArrayIterator?
      // https://bugs.ecmascript.org/show_bug.cgi?id=2416
      //if (Array.isArray(list)) { usingIterator=false; }

      var length;
      var result, i, value;
      if (usingIterator) {
        i = 0;
        result = ES.IsCallable(this) ? Object(new this()) : [];
        var it = usingIterator ? ES.GetIterator(list) : null;
        var iterationValue;

        do {
          iterationValue = ES.IteratorNext(it);
          if (!iterationValue.done) {
            value = iterationValue.value;
            if (mapFn) {
              result[i] = hasThisArg ? mapFn.call(thisArg, value, i) : mapFn(value, i);
            } else {
              result[i] = value;
            }
            i += 1;
          }
        } while (!iterationValue.done);
        length = i;
      } else {
        length = ES.ToLength(list.length);
        result = ES.IsCallable(this) ? Object(new this(length)) : new Array(length);
        for (i = 0; i < length; ++i) {
          value = list[i];
          if (mapFn) {
            result[i] = hasThisArg ? mapFn.call(thisArg, value, i) : mapFn(value, i);
          } else {
            result[i] = value;
          }
        }
      }

      result.length = length;
      return result;
    },

    of: function () {
      return Array.from(arguments);
    }
  };
  defineProperties(Array, ArrayShims);

  var arrayFromSwallowsNegativeLengths = function () {
    try {
      return Array.from({ length: -1 }).length === 0;
    } catch (e) {
      return false;
    }
  };
  // Fixes a Firefox bug in v32
  // https://bugzilla.mozilla.org/show_bug.cgi?id=1063993
  if (!arrayFromSwallowsNegativeLengths()) {
    defineProperty(Array, 'from', ArrayShims.from, true);
  }

  // Our ArrayIterator is private; see
  // https://github.com/paulmillr/es6-shim/issues/252
  ArrayIterator = function (array, kind) {
      this.i = 0;
      this.array = array;
      this.kind = kind;
  };

  defineProperties(ArrayIterator.prototype, {
    next: function () {
      var i = this.i, array = this.array;
      if (!(this instanceof ArrayIterator)) {
        throw new TypeError('Not an ArrayIterator');
      }
      if (typeof array !== 'undefined') {
        var len = ES.ToLength(array.length);
        for (; i < len; i++) {
          var kind = this.kind;
          var retval;
          if (kind === 'key') {
            retval = i;
          } else if (kind === 'value') {
            retval = array[i];
          } else if (kind === 'entry') {
            retval = [i, array[i]];
          }
          this.i = i + 1;
          return { value: retval, done: false };
        }
      }
      this.array = void 0;
      return { value: void 0, done: true };
    }
  });
  addIterator(ArrayIterator.prototype);

  var ArrayPrototypeShims = {
    copyWithin: function (target, start) {
      var end = arguments[2]; // copyWithin.length must be 2
      var o = ES.ToObject(this);
      var len = ES.ToLength(o.length);
      target = ES.ToInteger(target);
      start = ES.ToInteger(start);
      var to = target < 0 ? Math.max(len + target, 0) : Math.min(target, len);
      var from = start < 0 ? Math.max(len + start, 0) : Math.min(start, len);
      end = typeof end === 'undefined' ? len : ES.ToInteger(end);
      var fin = end < 0 ? Math.max(len + end, 0) : Math.min(end, len);
      var count = Math.min(fin - from, len - to);
      var direction = 1;
      if (from < to && to < (from + count)) {
        direction = -1;
        from += count - 1;
        to += count - 1;
      }
      while (count > 0) {
        if (_hasOwnProperty.call(o, from)) {
          o[to] = o[from];
        } else {
          delete o[from];
        }
        from += direction;
        to += direction;
        count -= 1;
      }
      return o;
    },

    fill: function (value) {
      var start = arguments.length > 1 ? arguments[1] : void 0;
      var end = arguments.length > 2 ? arguments[2] : void 0;
      var O = ES.ToObject(this);
      var len = ES.ToLength(O.length);
      start = ES.ToInteger(typeof start === 'undefined' ? 0 : start);
      end = ES.ToInteger(typeof end === 'undefined' ? len : end);

      var relativeStart = start < 0 ? Math.max(len + start, 0) : Math.min(start, len);
      var relativeEnd = end < 0 ? len + end : end;

      for (var i = relativeStart; i < len && i < relativeEnd; ++i) {
        O[i] = value;
      }
      return O;
    },

    find: function find(predicate) {
      var list = ES.ToObject(this);
      var length = ES.ToLength(list.length);
      if (!ES.IsCallable(predicate)) {
        throw new TypeError('Array#find: predicate must be a function');
      }
      var thisArg = arguments[1];
      for (var i = 0, value; i < length; i++) {
        value = list[i];
        if (predicate.call(thisArg, value, i, list)) { return value; }
      }
      return;
    },

    findIndex: function findIndex(predicate) {
      var list = ES.ToObject(this);
      var length = ES.ToLength(list.length);
      if (!ES.IsCallable(predicate)) {
        throw new TypeError('Array#findIndex: predicate must be a function');
      }
      var thisArg = arguments[1];
      for (var i = 0; i < length; i++) {
        if (predicate.call(thisArg, list[i], i, list)) { return i; }
      }
      return -1;
    },

    keys: function () {
      return new ArrayIterator(this, 'key');
    },

    values: function () {
      return new ArrayIterator(this, 'value');
    },

    entries: function () {
      return new ArrayIterator(this, 'entry');
    }
  };
  // Safari 7.1 defines Array#keys and Array#entries natively,
  // but the resulting ArrayIterator objects don't have a "next" method.
  if (Array.prototype.keys && !ES.IsCallable([1].keys().next)) {
    delete Array.prototype.keys;
  }
  if (Array.prototype.entries && !ES.IsCallable([1].entries().next)) {
    delete Array.prototype.entries;
  }
  defineProperties(Array.prototype, ArrayPrototypeShims);

  addIterator(Array.prototype, function () { return this.values(); });
  // Chrome defines keys/values/entries on Array, but doesn't give us
  // any way to identify its iterator.  So add our own shimmed field.
  if (Object.getPrototypeOf) {
    addIterator(Object.getPrototypeOf([].values()));
  }

  var maxSafeInteger = Math.pow(2, 53) - 1;
  defineProperties(Number, {
    MAX_SAFE_INTEGER: maxSafeInteger,
    MIN_SAFE_INTEGER: -maxSafeInteger,
    EPSILON: 2.220446049250313e-16,

    parseInt: globals.parseInt,
    parseFloat: globals.parseFloat,

    isFinite: function (value) {
      return typeof value === 'number' && global_isFinite(value);
    },

    isInteger: function (value) {
      return Number.isFinite(value) &&
        ES.ToInteger(value) === value;
    },

    isSafeInteger: function (value) {
      return Number.isInteger(value) && Math.abs(value) <= Number.MAX_SAFE_INTEGER;
    },

    isNaN: function (value) {
      // NaN !== NaN, but they are identical.
      // NaNs are the only non-reflexive value, i.e., if x !== x,
      // then x is NaN.
      // isNaN is broken: it converts its argument to number, so
      // isNaN('foo') => true
      return value !== value;
    }

  });

  // Work around bugs in Array#find and Array#findIndex -- early
  // implementations skipped holes in sparse arrays. (Note that the
  // implementations of find/findIndex indirectly use shimmed
  // methods of Number, so this test has to happen down here.)
  if (![, 1].find(function (item, idx) { return idx === 0; })) {
    defineProperty(Array.prototype, 'find', ArrayPrototypeShims.find, true);
  }
  if ([, 1].findIndex(function (item, idx) { return idx === 0; }) !== 0) {
    defineProperty(Array.prototype, 'findIndex', ArrayPrototypeShims.findIndex, true);
  }

  if (supportsDescriptors) {
    defineProperties(Object, {
      getPropertyDescriptor: function (subject, name) {
        var pd = Object.getOwnPropertyDescriptor(subject, name);
        var proto = Object.getPrototypeOf(subject);
        while (typeof pd === 'undefined' && proto !== null) {
          pd = Object.getOwnPropertyDescriptor(proto, name);
          proto = Object.getPrototypeOf(proto);
        }
        return pd;
      },

      getPropertyNames: function (subject) {
        var result = Object.getOwnPropertyNames(subject);
        var proto = Object.getPrototypeOf(subject);

        var addProperty = function (property) {
          if (result.indexOf(property) === -1) {
            result.push(property);
          }
        };

        while (proto !== null) {
          Object.getOwnPropertyNames(proto).forEach(addProperty);
          proto = Object.getPrototypeOf(proto);
        }
        return result;
      }
    });

    defineProperties(Object, {
      // 19.1.3.1
      assign: function (target, source) {
        if (!ES.TypeIsObject(target)) {
          throw new TypeError('target must be an object');
        }
        return Array.prototype.reduce.call(arguments, function (target, source) {
          return Object.keys(Object(source)).reduce(function (target, key) {
            target[key] = source[key];
            return target;
          }, target);
        });
      },

      is: function (a, b) {
        return ES.SameValue(a, b);
      },

      // 19.1.3.9
      // shim from https://gist.github.com/WebReflection/5593554
      setPrototypeOf: (function (Object, magic) {
        var set;

        var checkArgs = function (O, proto) {
          if (!ES.TypeIsObject(O)) {
            throw new TypeError('cannot set prototype on a non-object');
          }
          if (!(proto === null || ES.TypeIsObject(proto))) {
            throw new TypeError('can only set prototype to an object or null' + proto);
          }
        };

        var setPrototypeOf = function (O, proto) {
          checkArgs(O, proto);
          set.call(O, proto);
          return O;
        };

        try {
          // this works already in Firefox and Safari
          set = Object.getOwnPropertyDescriptor(Object.prototype, magic).set;
          set.call({}, null);
        } catch (e) {
          if (Object.prototype !== {}[magic]) {
            // IE < 11 cannot be shimmed
            return;
          }
          // probably Chrome or some old Mobile stock browser
          set = function (proto) {
            this[magic] = proto;
          };
          // please note that this will **not** work
          // in those browsers that do not inherit
          // __proto__ by mistake from Object.prototype
          // in these cases we should probably throw an error
          // or at least be informed about the issue
          setPrototypeOf.polyfill = setPrototypeOf(
            setPrototypeOf({}, null),
            Object.prototype
          ) instanceof Object;
          // setPrototypeOf.polyfill === true means it works as meant
          // setPrototypeOf.polyfill === false means it's not 100% reliable
          // setPrototypeOf.polyfill === undefined
          // or
          // setPrototypeOf.polyfill ==  null means it's not a polyfill
          // which means it works as expected
          // we can even delete Object.prototype.__proto__;
        }
        return setPrototypeOf;
      })(Object, '__proto__')
    });
  }

  // Workaround bug in Opera 12 where setPrototypeOf(x, null) doesn't work,
  // but Object.create(null) does.
  if (Object.setPrototypeOf && Object.getPrototypeOf &&
      Object.getPrototypeOf(Object.setPrototypeOf({}, null)) !== null &&
      Object.getPrototypeOf(Object.create(null)) === null) {
    (function () {
      var FAKENULL = Object.create(null);
      var gpo = Object.getPrototypeOf, spo = Object.setPrototypeOf;
      Object.getPrototypeOf = function (o) {
        var result = gpo(o);
        return result === FAKENULL ? null : result;
      };
      Object.setPrototypeOf = function (o, p) {
        if (p === null) { p = FAKENULL; }
        return spo(o, p);
      };
      Object.setPrototypeOf.polyfill = false;
    })();
  }

  try {
    Object.keys('foo');
  } catch (e) {
    var originalObjectKeys = Object.keys;
    Object.keys = function (obj) {
      return originalObjectKeys(ES.ToObject(obj));
    };
  }

  var MathShims = {
    acosh: function (value) {
      value = Number(value);
      if (Number.isNaN(value) || value < 1) { return NaN; }
      if (value === 1) { return 0; }
      if (value === Infinity) { return value; }
      return Math.log(value + Math.sqrt(value * value - 1));
    },

    asinh: function (value) {
      value = Number(value);
      if (value === 0 || !global_isFinite(value)) {
        return value;
      }
      return value < 0 ? -Math.asinh(-value) : Math.log(value + Math.sqrt(value * value + 1));
    },

    atanh: function (value) {
      value = Number(value);
      if (Number.isNaN(value) || value < -1 || value > 1) {
        return NaN;
      }
      if (value === -1) { return -Infinity; }
      if (value === 1) { return Infinity; }
      if (value === 0) { return value; }
      return 0.5 * Math.log((1 + value) / (1 - value));
    },

    cbrt: function (value) {
      value = Number(value);
      if (value === 0) { return value; }
      var negate = value < 0, result;
      if (negate) { value = -value; }
      result = Math.pow(value, 1 / 3);
      return negate ? -result : result;
    },

    clz32: function (value) {
      // See https://bugs.ecmascript.org/show_bug.cgi?id=2465
      value = Number(value);
      var number = ES.ToUint32(value);
      if (number === 0) {
        return 32;
      }
      return 32 - (number).toString(2).length;
    },

    cosh: function (value) {
      value = Number(value);
      if (value === 0) { return 1; } // +0 or -0
      if (Number.isNaN(value)) { return NaN; }
      if (!global_isFinite(value)) { return Infinity; }
      if (value < 0) { value = -value; }
      if (value > 21) { return Math.exp(value) / 2; }
      return (Math.exp(value) + Math.exp(-value)) / 2;
    },

    expm1: function (value) {
      value = Number(value);
      if (value === -Infinity) { return -1; }
      if (!global_isFinite(value) || value === 0) { return value; }
      return Math.exp(value) - 1;
    },

    hypot: function (x, y) {
      var anyNaN = false;
      var allZero = true;
      var anyInfinity = false;
      var numbers = [];
      Array.prototype.every.call(arguments, function (arg) {
        var num = Number(arg);
        if (Number.isNaN(num)) {
          anyNaN = true;
        } else if (num === Infinity || num === -Infinity) {
          anyInfinity = true;
        } else if (num !== 0) {
          allZero = false;
        }
        if (anyInfinity) {
          return false;
        } else if (!anyNaN) {
          numbers.push(Math.abs(num));
        }
        return true;
      });
      if (anyInfinity) { return Infinity; }
      if (anyNaN) { return NaN; }
      if (allZero) { return 0; }

      numbers.sort(function (a, b) { return b - a; });
      var largest = numbers[0];
      var divided = numbers.map(function (number) { return number / largest; });
      var sum = divided.reduce(function (sum, number) { return sum += number * number; }, 0);
      return largest * Math.sqrt(sum);
    },

    log2: function (value) {
      return Math.log(value) * Math.LOG2E;
    },

    log10: function (value) {
      return Math.log(value) * Math.LOG10E;
    },

    log1p: function (value) {
      value = Number(value);
      if (value < -1 || Number.isNaN(value)) { return NaN; }
      if (value === 0 || value === Infinity) { return value; }
      if (value === -1) { return -Infinity; }
      var result = 0;
      var n = 50;

      if (value < 0 || value > 1) { return Math.log(1 + value); }
      for (var i = 1; i < n; i++) {
        if ((i % 2) === 0) {
          result -= Math.pow(value, i) / i;
        } else {
          result += Math.pow(value, i) / i;
        }
      }

      return result;
    },

    sign: function (value) {
      var number = +value;
      if (number === 0) { return number; }
      if (Number.isNaN(number)) { return number; }
      return number < 0 ? -1 : 1;
    },

    sinh: function (value) {
      value = Number(value);
      if (!global_isFinite(value) || value === 0) { return value; }
      return (Math.exp(value) - Math.exp(-value)) / 2;
    },

    tanh: function (value) {
      value = Number(value);
      if (Number.isNaN(value) || value === 0) { return value; }
      if (value === Infinity) { return 1; }
      if (value === -Infinity) { return -1; }
      return (Math.exp(value) - Math.exp(-value)) / (Math.exp(value) + Math.exp(-value));
    },

    trunc: function (value) {
      var number = Number(value);
      return number < 0 ? -Math.floor(-number) : Math.floor(number);
    },

    imul: function (x, y) {
      // taken from https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/imul
      x = ES.ToUint32(x);
      y = ES.ToUint32(y);
      var ah  = (x >>> 16) & 0xffff;
      var al = x & 0xffff;
      var bh  = (y >>> 16) & 0xffff;
      var bl = y & 0xffff;
      // the shift by 0 fixes the sign on the high part
      // the final |0 converts the unsigned value into a signed value
      return ((al * bl) + (((ah * bl + al * bh) << 16) >>> 0)|0);
    },

    fround: function (x) {
      if (x === 0 || x === Infinity || x === -Infinity || Number.isNaN(x)) {
        return x;
      }
      var num = Number(x);
      return numberConversion.toFloat32(num);
    }
  };
  defineProperties(Math, MathShims);

  if (Math.imul(0xffffffff, 5) !== -5) {
    // Safari 6.1, at least, reports "0" for this value
    Math.imul = MathShims.imul;
  }

  // Promises
  // Simplest possible implementation; use a 3rd-party library if you
  // want the best possible speed and/or long stack traces.
  var PromiseShim = (function () {

    var Promise, Promise$prototype;

    ES.IsPromise = function (promise) {
      if (!ES.TypeIsObject(promise)) {
        return false;
      }
      if (!promise._promiseConstructor) {
        // _promiseConstructor is a bit more unique than _status, so we'll
        // check that instead of the [[PromiseStatus]] internal field.
        return false;
      }
      if (typeof promise._status === 'undefined') {
        return false; // uninitialized
      }
      return true;
    };

    // "PromiseCapability" in the spec is what most promise implementations
    // call a "deferred".
    var PromiseCapability = function (C) {
      if (!ES.IsCallable(C)) {
        throw new TypeError('bad promise constructor');
      }
      var capability = this;
      var resolver = function (resolve, reject) {
        capability.resolve = resolve;
        capability.reject = reject;
      };
      capability.promise = ES.Construct(C, [resolver]);
      // see https://bugs.ecmascript.org/show_bug.cgi?id=2478
      if (!capability.promise._es6construct) {
        throw new TypeError('bad promise constructor');
      }
      if (!(ES.IsCallable(capability.resolve) &&
            ES.IsCallable(capability.reject))) {
        throw new TypeError('bad promise constructor');
      }
    };

    // find an appropriate setImmediate-alike
    var setTimeout = globals.setTimeout;
    var makeZeroTimeout;
    if (typeof window !== 'undefined' && ES.IsCallable(window.postMessage)) {
      makeZeroTimeout = function () {
        // from http://dbaron.org/log/20100309-faster-timeouts
        var timeouts = [];
        var messageName = 'zero-timeout-message';
        var setZeroTimeout = function (fn) {
          timeouts.push(fn);
          window.postMessage(messageName, '*');
        };
        var handleMessage = function (event) {
          if (event.source == window && event.data == messageName) {
            event.stopPropagation();
            if (timeouts.length === 0) { return; }
            var fn = timeouts.shift();
            fn();
          }
        };
        window.addEventListener('message', handleMessage, true);
        return setZeroTimeout;
      };
    }
    var makePromiseAsap = function () {
      // An efficient task-scheduler based on a pre-existing Promise
      // implementation, which we can use even if we override the
      // global Promise below (in order to workaround bugs)
      // https://github.com/Raynos/observ-hash/issues/2#issuecomment-35857671
      var P = globals.Promise;
      return P && P.resolve && function (task) {
        return P.resolve().then(task);
      };
    };
    var enqueue = ES.IsCallable(globals.setImmediate) ?
      globals.setImmediate.bind(globals) :
      typeof process === 'object' && process.nextTick ? process.nextTick :
      makePromiseAsap() ||
      (ES.IsCallable(makeZeroTimeout) ? makeZeroTimeout() :
      function (task) { setTimeout(task, 0); }); // fallback

    var triggerPromiseReactions = function (reactions, x) {
      reactions.forEach(function (reaction) {
        enqueue(function () {
          // PromiseReactionTask
          var handler = reaction.handler;
          var capability = reaction.capability;
          var resolve = capability.resolve;
          var reject = capability.reject;
          try {
            var result = handler(x);
            if (result === capability.promise) {
              throw new TypeError('self resolution');
            }
            var updateResult =
              updatePromiseFromPotentialThenable(result, capability);
            if (!updateResult) {
              resolve(result);
            }
          } catch (e) {
            reject(e);
          }
        });
      });
    };

    var updatePromiseFromPotentialThenable = function (x, capability) {
      if (!ES.TypeIsObject(x)) {
        return false;
      }
      var resolve = capability.resolve;
      var reject = capability.reject;
      try {
        var then = x.then; // only one invocation of accessor
        if (!ES.IsCallable(then)) { return false; }
        then.call(x, resolve, reject);
      } catch (e) {
        reject(e);
      }
      return true;
    };

    var promiseResolutionHandler = function (promise, onFulfilled, onRejected) {
      return function (x) {
        if (x === promise) {
          return onRejected(new TypeError('self resolution'));
        }
        var C = promise._promiseConstructor;
        var capability = new PromiseCapability(C);
        var updateResult = updatePromiseFromPotentialThenable(x, capability);
        if (updateResult) {
          return capability.promise.then(onFulfilled, onRejected);
        } else {
          return onFulfilled(x);
        }
      };
    };

    Promise = function (resolver) {
      var promise = this;
      promise = emulateES6construct(promise);
      if (!promise._promiseConstructor) {
        // we use _promiseConstructor as a stand-in for the internal
        // [[PromiseStatus]] field; it's a little more unique.
        throw new TypeError('bad promise');
      }
      if (typeof promise._status !== 'undefined') {
        throw new TypeError('promise already initialized');
      }
      // see https://bugs.ecmascript.org/show_bug.cgi?id=2482
      if (!ES.IsCallable(resolver)) {
        throw new TypeError('not a valid resolver');
      }
      promise._status = 'unresolved';
      promise._resolveReactions = [];
      promise._rejectReactions = [];

      var resolve = function (resolution) {
        if (promise._status !== 'unresolved') { return; }
        var reactions = promise._resolveReactions;
        promise._result = resolution;
        promise._resolveReactions = void 0;
        promise._rejectReactions = void 0;
        promise._status = 'has-resolution';
        triggerPromiseReactions(reactions, resolution);
      };
      var reject = function (reason) {
        if (promise._status !== 'unresolved') { return; }
        var reactions = promise._rejectReactions;
        promise._result = reason;
        promise._resolveReactions = void 0;
        promise._rejectReactions = void 0;
        promise._status = 'has-rejection';
        triggerPromiseReactions(reactions, reason);
      };
      try {
        resolver(resolve, reject);
      } catch (e) {
        reject(e);
      }
      return promise;
    };
    Promise$prototype = Promise.prototype;
    defineProperties(Promise, {
      '@@create': function (obj) {
        var constructor = this;
        // AllocatePromise
        // The `obj` parameter is a hack we use for es5
        // compatibility.
        var prototype = constructor.prototype || Promise$prototype;
        obj = obj || create(prototype);
        defineProperties(obj, {
          _status: void 0,
          _result: void 0,
          _resolveReactions: void 0,
          _rejectReactions: void 0,
          _promiseConstructor: void 0
        });
        obj._promiseConstructor = constructor;
        return obj;
      }
    });

    var _promiseAllResolver = function (index, values, capability, remaining) {
      var done = false;
      return function (x) {
        if (done) { return; } // protect against being called multiple times
        done = true;
        values[index] = x;
        if ((--remaining.count) === 0) {
          var resolve = capability.resolve;
          resolve(values); // call w/ this===undefined
        }
      };
    };

    Promise.all = function (iterable) {
      var C = this;
      var capability = new PromiseCapability(C);
      var resolve = capability.resolve;
      var reject = capability.reject;
      try {
        if (!ES.IsIterable(iterable)) {
          throw new TypeError('bad iterable');
        }
        var it = ES.GetIterator(iterable);
        var values = [], remaining = { count: 1 };
        for (var index = 0; ; index++) {
          var next = ES.IteratorNext(it);
          if (next.done) {
            break;
          }
          var nextPromise = C.resolve(next.value);
          var resolveElement = _promiseAllResolver(
            index, values, capability, remaining
          );
          remaining.count++;
          nextPromise.then(resolveElement, capability.reject);
        }
        if ((--remaining.count) === 0) {
          resolve(values); // call w/ this===undefined
        }
      } catch (e) {
        reject(e);
      }
      return capability.promise;
    };

    Promise.race = function (iterable) {
      var C = this;
      var capability = new PromiseCapability(C);
      var resolve = capability.resolve;
      var reject = capability.reject;
      try {
        if (!ES.IsIterable(iterable)) {
          throw new TypeError('bad iterable');
        }
        var it = ES.GetIterator(iterable);
        while (true) {
          var next = ES.IteratorNext(it);
          if (next.done) {
            // If iterable has no items, resulting promise will never
            // resolve; see:
            // https://github.com/domenic/promises-unwrapping/issues/75
            // https://bugs.ecmascript.org/show_bug.cgi?id=2515
            break;
          }
          var nextPromise = C.resolve(next.value);
          nextPromise.then(resolve, reject);
        }
      } catch (e) {
        reject(e);
      }
      return capability.promise;
    };

    Promise.reject = function (reason) {
      var C = this;
      var capability = new PromiseCapability(C);
      var reject = capability.reject;
      reject(reason); // call with this===undefined
      return capability.promise;
    };

    Promise.resolve = function (v) {
      var C = this;
      if (ES.IsPromise(v)) {
        var constructor = v._promiseConstructor;
        if (constructor === C) { return v; }
      }
      var capability = new PromiseCapability(C);
      var resolve = capability.resolve;
      resolve(v); // call with this===undefined
      return capability.promise;
    };

    Promise.prototype['catch'] = function (onRejected) {
      return this.then(void 0, onRejected);
    };

    Promise.prototype.then = function (onFulfilled, onRejected) {
      var promise = this;
      if (!ES.IsPromise(promise)) { throw new TypeError('not a promise'); }
      // this.constructor not this._promiseConstructor; see
      // https://bugs.ecmascript.org/show_bug.cgi?id=2513
      var C = this.constructor;
      var capability = new PromiseCapability(C);
      if (!ES.IsCallable(onRejected)) {
        onRejected = function (e) { throw e; };
      }
      if (!ES.IsCallable(onFulfilled)) {
        onFulfilled = function (x) { return x; };
      }
      var resolutionHandler =
        promiseResolutionHandler(promise, onFulfilled, onRejected);
      var resolveReaction =
        { capability: capability, handler: resolutionHandler };
      var rejectReaction =
        { capability: capability, handler: onRejected };
      switch (promise._status) {
      case 'unresolved':
        promise._resolveReactions.push(resolveReaction);
        promise._rejectReactions.push(rejectReaction);
        break;
      case 'has-resolution':
        triggerPromiseReactions([resolveReaction], promise._result);
        break;
      case 'has-rejection':
        triggerPromiseReactions([rejectReaction], promise._result);
        break;
      default:
        throw new TypeError('unexpected');
      }
      return capability.promise;
    };

    return Promise;
  })();
  // export the Promise constructor.
  defineProperties(globals, { Promise: PromiseShim });
  // In Chrome 33 (and thereabouts) Promise is defined, but the
  // implementation is buggy in a number of ways.  Let's check subclassing
  // support to see if we have a buggy implementation.
  var promiseSupportsSubclassing = supportsSubclassing(globals.Promise, function (S) {
    return S.resolve(42) instanceof S;
  });
  var promiseIgnoresNonFunctionThenCallbacks = (function () {
    try {
      globals.Promise.reject(42).then(null, 5).then(null, function () {});
      return true;
    } catch (ex) {
      return false;
    }
  }());
  var promiseRequiresObjectContext = (function () {
    try { Promise.call(3, function () {}); } catch (e) { return true; }
    return false;
  }());
  if (!promiseSupportsSubclassing || !promiseIgnoresNonFunctionThenCallbacks || !promiseRequiresObjectContext) {
    globals.Promise = PromiseShim;
  }

  // Map and Set require a true ES5 environment
  // Their fast path also requires that the environment preserve
  // property insertion order, which is not guaranteed by the spec.
  var testOrder = function (a) {
    var b = Object.keys(a.reduce(function (o, k) {
      o[k] = true;
      return o;
    }, {}));
    return a.join(':') === b.join(':');
  };
  var preservesInsertionOrder = testOrder(['z', 'a', 'bb']);
  // some engines (eg, Chrome) only preserve insertion order for string keys
  var preservesNumericInsertionOrder = testOrder(['z', 1, 'a', '3', 2]);

  if (supportsDescriptors) {

    var fastkey = function fastkey(key) {
      if (!preservesInsertionOrder) {
        return null;
      }
      var type = typeof key;
      if (type === 'string') {
        return '$' + key;
      } else if (type === 'number') {
        // note that -0 will get coerced to "0" when used as a property key
        if (!preservesNumericInsertionOrder) {
          return 'n' + key;
        }
        return key;
      }
      return null;
    };

    var emptyObject = function emptyObject() {
      // accomodate some older not-quite-ES5 browsers
      return Object.create ? Object.create(null) : {};
    };

    var collectionShims = {
      Map: (function () {

        var empty = {};

        function MapEntry(key, value) {
          this.key = key;
          this.value = value;
          this.next = null;
          this.prev = null;
        }

        MapEntry.prototype.isRemoved = function () {
          return this.key === empty;
        };

        function MapIterator(map, kind) {
          this.head = map._head;
          this.i = this.head;
          this.kind = kind;
        }

        MapIterator.prototype = {
          next: function () {
            var i = this.i, kind = this.kind, head = this.head, result;
            if (typeof this.i === 'undefined') {
              return { value: void 0, done: true };
            }
            while (i.isRemoved() && i !== head) {
              // back up off of removed entries
              i = i.prev;
            }
            // advance to next unreturned element.
            while (i.next !== head) {
              i = i.next;
              if (!i.isRemoved()) {
                if (kind === 'key') {
                  result = i.key;
                } else if (kind === 'value') {
                  result = i.value;
                } else {
                  result = [i.key, i.value];
                }
                this.i = i;
                return { value: result, done: false };
              }
            }
            // once the iterator is done, it is done forever.
            this.i = void 0;
            return { value: void 0, done: true };
          }
        };
        addIterator(MapIterator.prototype);

        function Map(iterable) {
          var map = this;
          map = emulateES6construct(map);
          if (!map._es6map) {
            throw new TypeError('bad map');
          }

          var head = new MapEntry(null, null);
          // circular doubly-linked list.
          head.next = head.prev = head;

          defineProperties(map, {
            _head: head,
            _storage: emptyObject(),
            _size: 0
          });

          // Optionally initialize map from iterable
          if (typeof iterable !== 'undefined' && iterable !== null) {
            var it = ES.GetIterator(iterable);
            var adder = map.set;
            if (!ES.IsCallable(adder)) { throw new TypeError('bad map'); }
            while (true) {
              var next = ES.IteratorNext(it);
              if (next.done) { break; }
              var nextItem = next.value;
              if (!ES.TypeIsObject(nextItem)) {
                throw new TypeError('expected iterable of pairs');
              }
              adder.call(map, nextItem[0], nextItem[1]);
            }
          }
          return map;
        }
        var Map$prototype = Map.prototype;
        defineProperties(Map, {
          '@@create': function (obj) {
            var constructor = this;
            var prototype = constructor.prototype || Map$prototype;
            obj = obj || create(prototype);
            defineProperties(obj, { _es6map: true });
            return obj;
          }
        });

        Object.defineProperty(Map.prototype, 'size', {
          configurable: true,
          enumerable: false,
          get: function () {
            if (typeof this._size === 'undefined') {
              throw new TypeError('size method called on incompatible Map');
            }
            return this._size;
          }
        });

        defineProperties(Map.prototype, {
          get: function (key) {
            var fkey = fastkey(key);
            if (fkey !== null) {
              // fast O(1) path
              var entry = this._storage[fkey];
              if (entry) {
                return entry.value;
              } else {
                return;
              }
            }
            var head = this._head, i = head;
            while ((i = i.next) !== head) {
              if (ES.SameValueZero(i.key, key)) {
                return i.value;
              }
            }
            return;
          },

          has: function (key) {
            var fkey = fastkey(key);
            if (fkey !== null) {
              // fast O(1) path
              return typeof this._storage[fkey] !== 'undefined';
            }
            var head = this._head, i = head;
            while ((i = i.next) !== head) {
              if (ES.SameValueZero(i.key, key)) {
                return true;
              }
            }
            return false;
          },

          set: function (key, value) {
            var head = this._head, i = head, entry;
            var fkey = fastkey(key);
            if (fkey !== null) {
              // fast O(1) path
              if (typeof this._storage[fkey] !== 'undefined') {
                this._storage[fkey].value = value;
                return;
              } else {
                entry = this._storage[fkey] = new MapEntry(key, value);
                i = head.prev;
                // fall through
              }
            }
            while ((i = i.next) !== head) {
              if (ES.SameValueZero(i.key, key)) {
                i.value = value;
                return;
              }
            }
            entry = entry || new MapEntry(key, value);
            if (ES.SameValue(-0, key)) {
              entry.key = +0; // coerce -0 to +0 in entry
            }
            entry.next = this._head;
            entry.prev = this._head.prev;
            entry.prev.next = entry;
            entry.next.prev = entry;
            this._size += 1;
            return this;
          },

          'delete': function (key) {
            var head = this._head, i = head;
            var fkey = fastkey(key);
            if (fkey !== null) {
              // fast O(1) path
              if (typeof this._storage[fkey] === 'undefined') {
                return false;
              }
              i = this._storage[fkey].prev;
              delete this._storage[fkey];
              // fall through
            }
            while ((i = i.next) !== head) {
              if (ES.SameValueZero(i.key, key)) {
                i.key = i.value = empty;
                i.prev.next = i.next;
                i.next.prev = i.prev;
                this._size -= 1;
                return true;
              }
            }
            return false;
          },

          clear: function () {
            this._size = 0;
            this._storage = emptyObject();
            var head = this._head, i = head, p = i.next;
            while ((i = p) !== head) {
              i.key = i.value = empty;
              p = i.next;
              i.next = i.prev = head;
            }
            head.next = head.prev = head;
          },

          keys: function () {
            return new MapIterator(this, 'key');
          },

          values: function () {
            return new MapIterator(this, 'value');
          },

          entries: function () {
            return new MapIterator(this, 'key+value');
          },

          forEach: function (callback) {
            var context = arguments.length > 1 ? arguments[1] : null;
            var it = this.entries();
            for (var entry = it.next(); !entry.done; entry = it.next()) {
              callback.call(context, entry.value[1], entry.value[0], this);
            }
          }
        });
        addIterator(Map.prototype, function () { return this.entries(); });

        return Map;
      })(),

      Set: (function () {
        // Creating a Map is expensive.  To speed up the common case of
        // Sets containing only string or numeric keys, we use an object
        // as backing storage and lazily create a full Map only when
        // required.
        var SetShim = function Set(iterable) {
          var set = this;
          set = emulateES6construct(set);
          if (!set._es6set) {
            throw new TypeError('bad set');
          }

          defineProperties(set, {
            '[[SetData]]': null,
            _storage: emptyObject()
          });

          // Optionally initialize map from iterable
          if (typeof iterable !== 'undefined' && iterable !== null) {
            var it = ES.GetIterator(iterable);
            var adder = set.add;
            if (!ES.IsCallable(adder)) { throw new TypeError('bad set'); }
            while (true) {
              var next = ES.IteratorNext(it);
              if (next.done) { break; }
              var nextItem = next.value;
              adder.call(set, nextItem);
            }
          }
          return set;
        };
        var Set$prototype = SetShim.prototype;
        defineProperties(SetShim, {
          '@@create': function (obj) {
            var constructor = this;
            var prototype = constructor.prototype || Set$prototype;
            obj = obj || create(prototype);
            defineProperties(obj, { _es6set: true });
            return obj;
          }
        });

        // Switch from the object backing storage to a full Map.
        var ensureMap = function ensureMap(set) {
          if (!set['[[SetData]]']) {
            var m = set['[[SetData]]'] = new collectionShims.Map();
            Object.keys(set._storage).forEach(function (k) {
              // fast check for leading '$'
              if (k.charCodeAt(0) === 36) {
                k = k.slice(1);
              } else if (k.charAt(0) === 'n') {
                k = +k.slice(1);
              } else {
                k = +k;
              }
              m.set(k, k);
            });
            set._storage = null; // free old backing storage
          }
        };

        Object.defineProperty(SetShim.prototype, 'size', {
          configurable: true,
          enumerable: false,
          get: function () {
            if (typeof this._storage === 'undefined') {
              // https://github.com/paulmillr/es6-shim/issues/176
              throw new TypeError('size method called on incompatible Set');
            }
            ensureMap(this);
            return this['[[SetData]]'].size;
          }
        });

        defineProperties(SetShim.prototype, {
          has: function (key) {
            var fkey;
            if (this._storage && (fkey = fastkey(key)) !== null) {
              return !!this._storage[fkey];
            }
            ensureMap(this);
            return this['[[SetData]]'].has(key);
          },

          add: function (key) {
            var fkey;
            if (this._storage && (fkey = fastkey(key)) !== null) {
              this._storage[fkey] = true;
              return;
            }
            ensureMap(this);
            this['[[SetData]]'].set(key, key);
            return this;
          },

          'delete': function (key) {
            var fkey;
            if (this._storage && (fkey = fastkey(key)) !== null) {
              var hasFKey = _hasOwnProperty.call(this._storage, fkey);
              return (delete this._storage[fkey]) && hasFKey;
            }
            ensureMap(this);
            return this['[[SetData]]']['delete'](key);
          },

          clear: function () {
            if (this._storage) {
              this._storage = emptyObject();
              return;
            }
            return this['[[SetData]]'].clear();
          },

          keys: function () {
            ensureMap(this);
            return this['[[SetData]]'].keys();
          },

          values: function () {
            ensureMap(this);
            return this['[[SetData]]'].values();
          },

          entries: function () {
            ensureMap(this);
            return this['[[SetData]]'].entries();
          },

          forEach: function (callback) {
            var context = arguments.length > 1 ? arguments[1] : null;
            var entireSet = this;
            ensureMap(this);
            this['[[SetData]]'].forEach(function (value, key) {
              callback.call(context, key, key, entireSet);
            });
          }
        });
        addIterator(SetShim.prototype, function () { return this.values(); });

        return SetShim;
      })()
    };
    defineProperties(globals, collectionShims);

    if (globals.Map || globals.Set) {
      /*
        - In Firefox < 23, Map#size is a function.
        - In all current Firefox, Set#entries/keys/values & Map#clear do not exist
        - https://bugzilla.mozilla.org/show_bug.cgi?id=869996
        - In Firefox 24, Map and Set do not implement forEach
        - In Firefox 25 at least, Map and Set are callable without "new"
      */
      if (
        typeof globals.Map.prototype.clear !== 'function' ||
        new globals.Set().size !== 0 ||
        new globals.Map().size !== 0 ||
        typeof globals.Map.prototype.keys !== 'function' ||
        typeof globals.Set.prototype.keys !== 'function' ||
        typeof globals.Map.prototype.forEach !== 'function' ||
        typeof globals.Set.prototype.forEach !== 'function' ||
        isCallableWithoutNew(globals.Map) ||
        isCallableWithoutNew(globals.Set) ||
        !supportsSubclassing(globals.Map, function (M) {
          var m = new M([]);
          // Firefox 32 is ok with the instantiating the subclass but will
          // throw when the map is used.
          m.set(42, 42);
          return m instanceof M;
        })
      ) {
        globals.Map = collectionShims.Map;
        globals.Set = collectionShims.Set;
      }
    }
    // Shim incomplete iterator implementations.
    addIterator(Object.getPrototypeOf((new globals.Map()).keys()));
    addIterator(Object.getPrototypeOf((new globals.Set()).keys()));
  }

  return globals;
}));