es6-shim.js

// ES6-shim 0.13.0 (c) 2013-2014 Paul Miller (http://paulmillr.com)
// ES6-shim may be freely distributed under the MIT license.
// For more details and documentation:
// https://github.com/paulmillr/es6-shim/

(function(undefined) {
  '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 main = function() {
    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

    // 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];
        if (name in object) return;
        if (supportsDescriptors) {
          Object.defineProperty(object, name, {
            configurable: true,
            enumerable: false,
            writable: true,
            value: method
          });
        } else {
          object[name] = method;
        }
      });
    };

    // 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 === 'object' && 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);
    };

    // 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 Math.sign(number) * 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) &&
          (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() {
        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 (next === undefined) {
            break;
          }
          nextSub = String(next);
          stringElements.push(nextSub);
          nextIndex++;
        }
        return stringElements.join('');
      }
    });

    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] : undefined;
        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] : undefined;
        var pos = 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] : undefined;
        // 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 undefined;
        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 trimBeginRegexp = new RegExp('^[' + ws + '][' + ws + ']*');
      var trimEndRegexp = new RegExp('[' + ws + '][' + ws + ']*$');
      defineProperties(String.prototype, {
        trim: function() {
          if (this === undefined || this === null) {
            throw new TypeError("can't convert " + this + " to object");
          }
          return String(this)
            .replace(trimBeginRegexp, "")
            .replace(trimEndRegexp, "");
          }
      });
    }

    // 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 (s === undefined || i >= s.length) {
        this._s = undefined;
        return { value: undefined, 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;
    }

    defineProperties(Array, {
      from: function(iterable) {
        var mapFn = arguments.length > 1 ? arguments[1] : undefined;
        var thisArg = arguments.length > 2 ? arguments[2] : undefined;

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

        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 = usingIterator ? 0 : ES.ToLength(list.length);
        var result = ES.IsCallable(this) ? Object(usingIterator ? new this() : new this(length)) : new Array(length);
        var it = usingIterator ? ES.GetIterator(list) : null;
        var value;

        for (var i = 0; usingIterator || (i < length); i++) {
          if (usingIterator) {
            value = ES.IteratorNext(it);
            if (value.done) {
              length = i;
              break;
            }
            value = value.value;
          } else {
            value = list[i];
          }
          if (mapFn) {
            result[i] = thisArg ? mapFn.call(thisArg, value, i) : mapFn(value, i);
          } else {
            result[i] = value;
          }
        }

        result.length = length;
        return result;
      },

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

    // 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 (i === undefined || this.kind === undefined) {
          throw new TypeError('Not an ArrayIterator');
        }
        if (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 = undefined;
        return { value: undefined, done: true };
      }
    });
    addIterator(ArrayIterator.prototype);

    defineProperties(Array.prototype, {
      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 = (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] : undefined;
        var end = arguments.length > 2 ? arguments[2] : undefined;
        var O = ES.ToObject(this);
        var len = ES.ToLength(O.length);
        start = ES.ToInteger(start === undefined ? 0 : start);
        end = ES.ToInteger(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(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++) {
          if (i in list) {
            value = list[i];
            if (predicate.call(thisArg, value, i, list)) return value;
          }
        }
        return undefined;
      },

      findIndex: function(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 (i in list) {
            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");
      }
    });
    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;
      }

    });

    if (supportsDescriptors) {
      defineProperties(Object, {
        getPropertyDescriptor: function(subject, name) {
          var pd = Object.getOwnPropertyDescriptor(subject, name);
          var proto = Object.getPrototypeOf(subject);
          while (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) {
            if (!ES.TypeIsObject(source)) {
              throw new TypeError('source must be an object');
            }
            return Object.keys(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
        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 (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 (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 = undefined;
          promise._rejectReactions = undefined;
          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 = undefined;
          promise._rejectReactions = undefined;
          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: undefined,
            _result: undefined,
            _resolveReactions: undefined,
            _rejectReactions: undefined,
            _promiseConstructor: undefined
          });
          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(undefined, 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;
      }
    }());
    if (!promiseSupportsSubclassing || !promiseIgnoresNonFunctionThenCallbacks) {
      globals.Promise = PromiseShim;
    }

    // Map and Set require a true ES5 environment
    if (supportsDescriptors) {

      var fastkey = function fastkey(key) {
        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
          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 (this.i === undefined) {
                return { value: undefined, 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 = undefined;
              return { value: undefined, 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 (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];
                return entry ? entry.value : undefined;
              }
              var head = this._head, i = head;
              while ((i = i.next) !== head) {
                if (ES.SameValueZero(i.key, key)) {
                  return i.value;
                }
              }
              return undefined;
            },

            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;
            },

            '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 (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 {
                  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);
              return this['[[SetData]]'].set(key, key);
            },

            'delete': function(key) {
              var fkey;
              if (this._storage && (fkey = fastkey(key)) !== null) {
                delete this._storage[fkey];
                return;
              }
              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) {
            return (new 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()));
    }
  };

  if (typeof define === 'function' && define.amd) {
    define(main); // RequireJS
  } else {
    main(); // CommonJS and <script>
  }
})();