Synnefo

//     Underscore.js 1.2.3

//     (c) 2009-2011 Jeremy Ashkenas, DocumentCloud Inc.

//     Underscore is freely distributable under the MIT license.

//     Portions of Underscore are inspired or borrowed from Prototype,

//     Oliver Steele's Functional, and John Resig's Micro-Templating.

//     For all details and documentation:

//     http://documentcloud.github.com/underscore

(function() {

  // Baseline setup

  // --------------

  // Establish the root object, `window` in the browser, or `global` on the server.

  var root = this;

  // Save the previous value of the `_` variable.

  var previousUnderscore = root._;

  // Establish the object that gets returned to break out of a loop iteration.

  var breaker = {};

  // Save bytes in the minified (but not gzipped) version:

  var ArrayProto = Array.prototype, ObjProto = Object.prototype, FuncProto = Function.prototype;

  // Create quick reference variables for speed access to core prototypes.

  var slice            = ArrayProto.slice,

      concat           = ArrayProto.concat,

      unshift          = ArrayProto.unshift,

      toString         = ObjProto.toString,

      hasOwnProperty   = ObjProto.hasOwnProperty;

  // All **ECMAScript 5** native function implementations that we hope to use

  // are declared here.

  var

    nativeForEach      = ArrayProto.forEach,

    nativeMap          = ArrayProto.map,

    nativeReduce       = ArrayProto.reduce,

    nativeReduceRight  = ArrayProto.reduceRight,

    nativeFilter       = ArrayProto.filter,

    nativeEvery        = ArrayProto.every,

    nativeSome         = ArrayProto.some,

    nativeIndexOf      = ArrayProto.indexOf,

    nativeLastIndexOf  = ArrayProto.lastIndexOf,

    nativeIsArray      = Array.isArray,

    nativeKeys         = Object.keys,

    nativeBind         = FuncProto.bind;

  // Create a safe reference to the Underscore object for use below.

  var _ = function(obj) { return new wrapper(obj); };

  // Export the Underscore object for **Node.js** and **"CommonJS"**, with

  // backwards-compatibility for the old `require()` API. If we're not in

  // CommonJS, add `_` to the global object.

  if (typeof exports !== 'undefined') {

    if (typeof module !== 'undefined' && module.exports) {

      exports = module.exports = _;

    }

    exports._ = _;

  } else if (typeof define === 'function' && define.amd) {

    // Register as a named module with AMD.

    define('underscore', function() {

      return _;

    });

  } else {

    // Exported as a string, for Closure Compiler "advanced" mode.

    root['_'] = _;

  }

  // Current version.

  _.VERSION = '1.2.3';

  // Collection Functions

  // --------------------

  // The cornerstone, an `each` implementation, aka `forEach`.

  // Handles objects with the built-in `forEach`, arrays, and raw objects.

  // Delegates to **ECMAScript 5**'s native `forEach` if available.

  var each = _.each = _.forEach = function(obj, iterator, context) {

    if (obj == null) return;

    if (nativeForEach && obj.forEach === nativeForEach) {

      obj.forEach(iterator, context);

    } else if (obj.length === +obj.length) {

      for (var i = 0, l = obj.length; i < l; i++) {

        if (i in obj && iterator.call(context, obj[i], i, obj) === breaker) return;

      }

    } else {

      for (var key in obj) {

        if (hasOwnProperty.call(obj, key)) {

          if (iterator.call(context, obj[key], key, obj) === breaker) return;

        }

      }

    }

  };

  // Return the results of applying the iterator to each element.

  // Delegates to **ECMAScript 5**'s native `map` if available.

  _.map = function(obj, iterator, context) {

    var results = [];

    if (obj == null) return results;

    if (nativeMap && obj.map === nativeMap) return obj.map(iterator, context);

    each(obj, function(value, index, list) {

      results[results.length] = iterator.call(context, value, index, list);

    });

    return results;

  };

  // **Reduce** builds up a single result from a list of values, aka `inject`,

  // or `foldl`. Delegates to **ECMAScript 5**'s native `reduce` if available.

  _.reduce = _.foldl = _.inject = function(obj, iterator, memo, context) {

    var initial = arguments.length > 2;

    if (obj == null) obj = [];

    if (nativeReduce && obj.reduce === nativeReduce) {

      if (context) iterator = _.bind(iterator, context);

      return initial ? obj.reduce(iterator, memo) : obj.reduce(iterator);

    }

    each(obj, function(value, index, list) {

      if (!initial) {

        memo = value;

        initial = true;

      } else {

        memo = iterator.call(context, memo, value, index, list);

      }

    });

    if (!initial) throw new TypeError('Reduce of empty array with no initial value');

    return memo;

  };

  // The right-associative version of reduce, also known as `foldr`.

  // Delegates to **ECMAScript 5**'s native `reduceRight` if available.

  _.reduceRight = _.foldr = function(obj, iterator, memo, context) {

    var initial = arguments.length > 2;

    if (obj == null) obj = [];

    if (nativeReduceRight && obj.reduceRight === nativeReduceRight) {

      if (context) iterator = _.bind(iterator, context);

      return initial ? obj.reduceRight(iterator, memo) : obj.reduceRight(iterator);

    }

    var reversed = _.toArray(obj).reverse();

    if (context && !initial) iterator = _.bind(iterator, context);

    return initial ? _.reduce(reversed, iterator, memo, context) : _.reduce(reversed, iterator);

  };

  // Return the first value which passes a truth test. Aliased as `detect`.

  _.find = _.detect = function(obj, iterator, context) {

    var result;

    any(obj, function(value, index, list) {

      if (iterator.call(context, value, index, list)) {

        result = value;

        return true;

      }

    });

    return result;

  };

  // Return all the elements that pass a truth test.

  // Delegates to **ECMAScript 5**'s native `filter` if available.

  // Aliased as `select`.

  _.filter = _.select = function(obj, iterator, context) {

    var results = [];

    if (obj == null) return results;

    if (nativeFilter && obj.filter === nativeFilter) return obj.filter(iterator, context);

    each(obj, function(value, index, list) {

      if (iterator.call(context, value, index, list)) results[results.length] = value;

    });

    return results;

  };

  // Return all the elements for which a truth test fails.

  _.reject = function(obj, iterator, context) {

    var results = [];

    if (obj == null) return results;

    each(obj, function(value, index, list) {

      if (!iterator.call(context, value, index, list)) results[results.length] = value;

    });

    return results;

  };

  // Determine whether all of the elements match a truth test.

  // Delegates to **ECMAScript 5**'s native `every` if available.

  // Aliased as `all`.

  _.every = _.all = function(obj, iterator, context) {

    var result = true;

    if (obj == null) return result;

    if (nativeEvery && obj.every === nativeEvery) return obj.every(iterator, context);

    each(obj, function(value, index, list) {

      if (!(result = result && iterator.call(context, value, index, list))) return breaker;

    });

    return result;

  };

  // Determine if at least one element in the object matches a truth test.

  // Delegates to **ECMAScript 5**'s native `some` if available.

  // Aliased as `any`.

  var any = _.some = _.any = function(obj, iterator, context) {

    iterator || (iterator = _.identity);

    var result = false;

    if (obj == null) return result;

    if (nativeSome && obj.some === nativeSome) return obj.some(iterator, context);

    each(obj, function(value, index, list) {

      if (result || (result = iterator.call(context, value, index, list))) return breaker;

    });

    return !!result;

  };

  // Determine if a given value is included in the array or object using `===`.

  // Aliased as `contains`.

  _.include = _.contains = function(obj, target) {

    var found = false;

    if (obj == null) return found;

    if (nativeIndexOf && obj.indexOf === nativeIndexOf) return obj.indexOf(target) != -1;

    found = any(obj, function(value) {

      return value === target;

    });

    return found;

  };

  // Invoke a method (with arguments) on every item in a collection.

  _.invoke = function(obj, method) {

    var args = slice.call(arguments, 2);

    return _.map(obj, function(value) {

      return (method.call ? method || value : value[method]).apply(value, args);

    });

  };

  // Convenience version of a common use case of `map`: fetching a property.

  _.pluck = function(obj, key) {

    return _.map(obj, function(value){ return value[key]; });

  };

  // Return the maximum element or (element-based computation).

  _.max = function(obj, iterator, context) {

    if (!iterator && _.isArray(obj)) return Math.max.apply(Math, obj);

    if (!iterator && _.isEmpty(obj)) return -Infinity;

    var result = {computed : -Infinity};

    each(obj, function(value, index, list) {

      var computed = iterator ? iterator.call(context, value, index, list) : value;

      computed >= result.computed && (result = {value : value, computed : computed});

    });

    return result.value;

  };

  // Return the minimum element (or element-based computation).

  _.min = function(obj, iterator, context) {

    if (!iterator && _.isArray(obj)) return Math.min.apply(Math, obj);

    if (!iterator && _.isEmpty(obj)) return Infinity;

    var result = {computed : Infinity};

    each(obj, function(value, index, list) {

      var computed = iterator ? iterator.call(context, value, index, list) : value;

      computed < result.computed && (result = {value : value, computed : computed});

    });

    return result.value;

  };

  // Shuffle an array.

  _.shuffle = function(obj) {

    var shuffled = [], rand;

    each(obj, function(value, index, list) {

      if (index == 0) {

        shuffled[0] = value;

      } else {

        rand = Math.floor(Math.random() * (index + 1));

        shuffled[index] = shuffled[rand];

        shuffled[rand] = value;

      }

    });

    return shuffled;

  };

  // Sort the object's values by a criterion produced by an iterator.

  _.sortBy = function(obj, iterator, context) {

    return _.pluck(_.map(obj, function(value, index, list) {

      return {

        value : value,

        criteria : iterator.call(context, value, index, list)

      };

    }).sort(function(left, right) {

      var a = left.criteria, b = right.criteria;

      return a < b ? -1 : a > b ? 1 : 0;

    }), 'value');

  };

  // Groups the object's values by a criterion. Pass either a string attribute

  // to group by, or a function that returns the criterion.

  _.groupBy = function(obj, val) {

    var result = {};

    var iterator = _.isFunction(val) ? val : function(obj) { return obj[val]; };

    each(obj, function(value, index) {

      var key = iterator(value, index);

      (result[key] || (result[key] = [])).push(value);

    });

    return result;

  };

  // Use a comparator function to figure out at what index an object should

  // be inserted so as to maintain order. Uses binary search.

  _.sortedIndex = function(array, obj, iterator) {

    iterator || (iterator = _.identity);

    var low = 0, high = array.length;

    while (low < high) {

      var mid = (low + high) >> 1;

      iterator(array[mid]) < iterator(obj) ? low = mid + 1 : high = mid;

    }

    return low;

  };

  // Safely convert anything iterable into a real, live array.

  _.toArray = function(iterable) {

    if (!iterable)                return [];

    if (iterable.toArray)         return iterable.toArray();

    if (_.isArray(iterable))      return slice.call(iterable);

    if (_.isArguments(iterable))  return slice.call(iterable);

    return _.values(iterable);

  };

  // Return the number of elements in an object.

  _.size = function(obj) {

    return _.toArray(obj).length;

  };

  // Array Functions

  // ---------------

  // Get the first element of an array. Passing **n** will return the first N

  // values in the array. Aliased as `head`. The **guard** check allows it to work

  // with `_.map`.

  _.first = _.head = function(array, n, guard) {

    return (n != null) && !guard ? slice.call(array, 0, n) : array[0];

  };

  // Returns everything but the last entry of the array. Especcialy useful on

  // the arguments object. Passing **n** will return all the values in

  // the array, excluding the last N. The **guard** check allows it to work with

  // `_.map`.

  _.initial = function(array, n, guard) {

    return slice.call(array, 0, array.length - ((n == null) || guard ? 1 : n));

  };

  // Get the last element of an array. Passing **n** will return the last N

  // values in the array. The **guard** check allows it to work with `_.map`.

  _.last = function(array, n, guard) {

    if ((n != null) && !guard) {

      return slice.call(array, Math.max(array.length - n, 0));

    } else {

      return array[array.length - 1];

    }

  };

  // Returns everything but the first entry of the array. Aliased as `tail`.

  // Especially useful on the arguments object. Passing an **index** will return

  // the rest of the values in the array from that index onward. The **guard**

  // check allows it to work with `_.map`.

  _.rest = _.tail = function(array, index, guard) {

    return slice.call(array, (index == null) || guard ? 1 : index);

  };

  // Trim out all falsy values from an array.

  _.compact = function(array) {

    return _.filter(array, function(value){ return !!value; });

  };

  // Return a completely flattened version of an array.

  _.flatten = function(array, shallow) {

    return _.reduce(array, function(memo, value) {

      if (_.isArray(value)) return memo.concat(shallow ? value : _.flatten(value));

      memo[memo.length] = value;

      return memo;

    }, []);

  };

  // Return a version of the array that does not contain the specified value(s).

  _.without = function(array) {

    return _.difference(array, slice.call(arguments, 1));

  };

  // Produce a duplicate-free version of the array. If the array has already

  // been sorted, you have the option of using a faster algorithm.

  // Aliased as `unique`.

  _.uniq = _.unique = function(array, isSorted, iterator) {

    var initial = iterator ? _.map(array, iterator) : array;

    var result = [];

    _.reduce(initial, function(memo, el, i) {

      if (0 == i || (isSorted === true ? _.last(memo) != el : !_.include(memo, el))) {

        memo[memo.length] = el;

        result[result.length] = array[i];

      }

      return memo;

    }, []);

    return result;

  };

  // Produce an array that contains the union: each distinct element from all of

  // the passed-in arrays.

  _.union = function() {

    return _.uniq(_.flatten(arguments, true));

  };

  // Produce an array that contains every item shared between all the

  // passed-in arrays. (Aliased as "intersect" for back-compat.)

  _.intersection = _.intersect = function(array) {

    var rest = slice.call(arguments, 1);

    return _.filter(_.uniq(array), function(item) {

      return _.every(rest, function(other) {

        return _.indexOf(other, item) >= 0;

      });

    });

  };

  // Take the difference between one array and a number of other arrays.

  // Only the elements present in just the first array will remain.

  _.difference = function(array) {

    var rest = _.flatten(slice.call(arguments, 1));

    return _.filter(array, function(value){ return !_.include(rest, value); });

  };

  // Zip together multiple lists into a single array -- elements that share

  // an index go together.

  _.zip = function() {

    var args = slice.call(arguments);

    var length = _.max(_.pluck(args, 'length'));

    var results = new Array(length);

    for (var i = 0; i < length; i++) results[i] = _.pluck(args, "" + i);

    return results;

  };

  // If the browser doesn't supply us with indexOf (I'm looking at you, **MSIE**),

  // we need this function. Return the position of the first occurrence of an

  // item in an array, or -1 if the item is not included in the array.

  // Delegates to **ECMAScript 5**'s native `indexOf` if available.

  // If the array is large and already in sort order, pass `true`

  // for **isSorted** to use binary search.

  _.indexOf = function(array, item, isSorted) {

    if (array == null) return -1;

    var i, l;

    if (isSorted) {

      i = _.sortedIndex(array, item);

      return array[i] === item ? i : -1;

    }

    if (nativeIndexOf && array.indexOf === nativeIndexOf) return array.indexOf(item);

    for (i = 0, l = array.length; i < l; i++) if (i in array && array[i] === item) return i;

    return -1;

  };

  // Delegates to **ECMAScript 5**'s native `lastIndexOf` if available.

  _.lastIndexOf = function(array, item) {

    if (array == null) return -1;

    if (nativeLastIndexOf && array.lastIndexOf === nativeLastIndexOf) return array.lastIndexOf(item);

    var i = array.length;

    while (i--) if (i in array && array[i] === item) return i;

    return -1;

  };

  // Generate an integer Array containing an arithmetic progression. A port of

  // the native Python `range()` function. See

  // [the Python documentation](http://docs.python.org/library/functions.html#range).

  _.range = function(start, stop, step) {

    if (arguments.length <= 1) {

      stop = start || 0;

      start = 0;

    }

    step = arguments[2] || 1;

    var len = Math.max(Math.ceil((stop - start) / step), 0);

    var idx = 0;

    var range = new Array(len);

    while(idx < len) {

      range[idx++] = start;

      start += step;

    }

    return range;

  };

  // Function (ahem) Functions

  // ------------------

  // Reusable constructor function for prototype setting.

  var ctor = function(){};

  // Create a function bound to a given object (assigning `this`, and arguments,

  // optionally). Binding with arguments is also known as `curry`.

  // Delegates to **ECMAScript 5**'s native `Function.bind` if available.

  // We check for `func.bind` first, to fail fast when `func` is undefined.

  _.bind = function bind(func, context) {

    var bound, args;

    if (func.bind === nativeBind && nativeBind) return nativeBind.apply(func, slice.call(arguments, 1));

    if (!_.isFunction(func)) throw new TypeError;

    args = slice.call(arguments, 2);

    return bound = function() {

      if (!(this instanceof bound)) return func.apply(context, args.concat(slice.call(arguments)));

      ctor.prototype = func.prototype;

      var self = new ctor;

      var result = func.apply(self, args.concat(slice.call(arguments)));

      if (Object(result) === result) return result;

      return self;

    };

  };

  // Bind all of an object's methods to that object. Useful for ensuring that

  // all callbacks defined on an object belong to it.

  _.bindAll = function(obj) {

    var funcs = slice.call(arguments, 1);

    if (funcs.length == 0) funcs = _.functions(obj);

    each(funcs, function(f) { obj[f] = _.bind(obj[f], obj); });

    return obj;

  };

  // Memoize an expensive function by storing its results.

  _.memoize = function(func, hasher) {

    var memo = {};

    hasher || (hasher = _.identity);

    return function() {

      var key = hasher.apply(this, arguments);

      return hasOwnProperty.call(memo, key) ? memo[key] : (memo[key] = func.apply(this, arguments));

    };

  };

  // Delays a function for the given number of milliseconds, and then calls

  // it with the arguments supplied.

  _.delay = function(func, wait) {

    var args = slice.call(arguments, 2);

    return setTimeout(function(){ return func.apply(func, args); }, wait);

  };

  // Defers a function, scheduling it to run after the current call stack has

  // cleared.

  _.defer = function(func) {

    return _.delay.apply(_, [func, 1].concat(slice.call(arguments, 1)));

  };

  // Returns a function, that, when invoked, will only be triggered at most once

  // during a given window of time.

  _.throttle = function(func, wait) {

    var context, args, timeout, throttling, more;

    var whenDone = _.debounce(function(){ more = throttling = false; }, wait);

    return function() {

      context = this; args = arguments;

      var later = function() {

        timeout = null;

        if (more) func.apply(context, args);

        whenDone();

      };

      if (!timeout) timeout = setTimeout(later, wait);

      if (throttling) {

        more = true;

      } else {

        func.apply(context, args);

      }

      whenDone();

      throttling = true;

    };

  };

  // Returns a function, that, as long as it continues to be invoked, will not

  // be triggered. The function will be called after it stops being called for

  // N milliseconds.

  _.debounce = function(func, wait) {

    var timeout;

    return function() {

      var context = this, args = arguments;

      var later = function() {

        timeout = null;

        func.apply(context, args);

      };

      clearTimeout(timeout);

      timeout = setTimeout(later, wait);

    };

  };

  // Returns a function that will be executed at most one time, no matter how

  // often you call it. Useful for lazy initialization.

  _.once = function(func) {

    var ran = false, memo;

    return function() {

      if (ran) return memo;

      ran = true;

      return memo = func.apply(this, arguments);

    };

  };

  // Returns the first function passed as an argument to the second,

  // allowing you to adjust arguments, run code before and after, and

  // conditionally execute the original function.

  _.wrap = function(func, wrapper) {

    return function() {

      var args = concat.apply([func], arguments);

      return wrapper.apply(this, args);

    };

  };

  // Returns a function that is the composition of a list of functions, each

  // consuming the return value of the function that follows.

  _.compose = function() {

    var funcs = arguments;

    return function() {

      var args = arguments;

      for (var i = funcs.length - 1; i >= 0; i--) {

        args = [funcs[i].apply(this, args)];

      }

      return args[0];

    };

  };

  // Returns a function that will only be executed after being called N times.

  _.after = function(times, func) {

    if (times <= 0) return func();

    return function() {

      if (--times < 1) { return func.apply(this, arguments); }

    };

  };

  // Object Functions

  // ----------------

  // Retrieve the names of an object's properties.

  // Delegates to **ECMAScript 5**'s native `Object.keys`

  _.keys = nativeKeys || function(obj) {

    if (obj !== Object(obj)) throw new TypeError('Invalid object');

    var keys = [];

    for (var key in obj) if (hasOwnProperty.call(obj, key)) keys[keys.length] = key;

    return keys;

  };

  // Retrieve the values of an object's properties.

  _.values = function(obj) {

    return _.map(obj, _.identity);

  };

  // Return a sorted list of the function names available on the object.

  // Aliased as `methods`

  _.functions = _.methods = function(obj) {

    var names = [];

    for (var key in obj) {

      if (_.isFunction(obj[key])) names.push(key);

    }

    return names.sort();

  };

  // Extend a given object with all the properties in passed-in object(s).

  _.extend = function(obj) {

    each(slice.call(arguments, 1), function(source) {

      for (var prop in source) {

        if (source[prop] !== void 0) obj[prop] = source[prop];

      }

    });

    return obj;

  };

  // Fill in a given object with default properties.

  _.defaults = function(obj) {

    each(slice.call(arguments, 1), function(source) {

      for (var prop in source) {

        if (obj[prop] == null) obj[prop] = source[prop];

      }

    });

    return obj;

  };

  // Create a (shallow-cloned) duplicate of an object.

  _.clone = function(obj) {

    if (!_.isObject(obj)) return obj;

    return _.isArray(obj) ? obj.slice() : _.extend({}, obj);

  };

  // Invokes interceptor with the obj, and then returns obj.

  // The primary purpose of this method is to "tap into" a method chain, in

  // order to perform operations on intermediate results within the chain.

  _.tap = function(obj, interceptor) {

    interceptor(obj);

    return obj;

  };

  // Internal recursive comparison function.

  function eq(a, b, stack) {

    // Identical objects are equal. `0 === -0`, but they aren't identical.

    // See the Harmony `egal` proposal: http://wiki.ecmascript.org/doku.php?id=harmony:egal.

    if (a === b) return a !== 0 || 1 / a == 1 / b;

    // A strict comparison is necessary because `null == undefined`.

    if (a == null || b == null) return a === b;

    // Unwrap any wrapped objects.

    if (a._chain) a = a._wrapped;

    if (b._chain) b = b._wrapped;

    // Invoke a custom `isEqual` method if one is provided.

    if (a.isEqual && _.isFunction(a.isEqual)) return a.isEqual(b);

    if (b.isEqual && _.isFunction(b.isEqual)) return b.isEqual(a);

    // Compare `[[Class]]` names.

    var className = toString.call(a);

    if (className != toString.call(b)) return false;

    switch (className) {

      // Strings, numbers, dates, and booleans are compared by value.

      case '[object String]':

        // Primitives and their corresponding object wrappers are equivalent; thus, `"5"` is

        // equivalent to `new String("5")`.

        return a == String(b);

      case '[object Number]':

        // `NaN`s are equivalent, but non-reflexive. An `egal` comparison is performed for

        // other numeric values.

        return a != +a ? b != +b : (a == 0 ? 1 / a == 1 / b : a == +b);

      case '[object Date]':

      case '[object Boolean]':

        // Coerce dates and booleans to numeric primitive values. Dates are compared by their

        // millisecond representations. Note that invalid dates with millisecond representations

        // of `NaN` are not equivalent.

        return +a == +b;

      // RegExps are compared by their source patterns and flags.

      case '[object RegExp]':

        return a.source == b.source &&

               a.global == b.global &&

               a.multiline == b.multiline &&

               a.ignoreCase == b.ignoreCase;

    }

    if (typeof a != 'object' || typeof b != 'object') return false;

    // Assume equality for cyclic structures. The algorithm for detecting cyclic

    // structures is adapted from ES 5.1 section 15.12.3, abstract operation `JO`.

    var length = stack.length;

    while (length--) {

      // Linear search. Performance is inversely proportional to the number of

      // unique nested structures.

      if (stack[length] == a) return true;

    }

    // Add the first object to the stack of traversed objects.

    stack.push(a);

    var size = 0, result = true;

    // Recursively compare objects and arrays.

    if (className == '[object Array]') {

      // Compare array lengths to determine if a deep comparison is necessary.

      size = a.length;

      result = size == b.length;

      if (result) {

        // Deep compare the contents, ignoring non-numeric properties.

        while (size--) {

          // Ensure commutative equality for sparse arrays.

          if (!(result = size in a == size in b && eq(a[size], b[size], stack))) break;

        }

      }

    } else {

      // Objects with different constructors are not equivalent.

      if ('constructor' in a != 'constructor' in b || a.constructor != b.constructor) return false;

      // Deep compare objects.

      for (var key in a) {

        if (hasOwnProperty.call(a, key)) {

          // Count the expected number of properties.

          size++;

          // Deep compare each member.

          if (!(result = hasOwnProperty.call(b, key) && eq(a[key], b[key], stack))) break;

        }

      }

      // Ensure that both objects contain the same number of properties.

      if (result) {

        for (key in b) {

          if (hasOwnProperty.call(b, key) && !(size--)) break;

        }

        result = !size;

      }

    }

    // Remove the first object from the stack of traversed objects.

    stack.pop();

    return result;

  }

  // Perform a deep comparison to check if two objects are equal.

  _.isEqual = function(a, b) {

    return eq(a, b, []);

  };

  // Is a given array, string, or object empty?

  // An "empty" object has no enumerable own-properties.

  _.isEmpty = function(obj) {

    if (_.isArray(obj) || _.isString(obj)) return obj.length === 0;

    for (var key in obj) if (hasOwnProperty.call(obj, key)) return false;

    return true;

  };

  // Is a given value a DOM element?

  _.isElement = function(obj) {

    return !!(obj && obj.nodeType == 1);

  };

  // Is a given value an array?

  // Delegates to ECMA5's native Array.isArray

  _.isArray = nativeIsArray || function(obj) {

    return toString.call(obj) == '[object Array]';

  };

  // Is a given variable an object?

  _.isObject = function(obj) {

    return obj === Object(obj);

  };

  // Is a given variable an arguments object?

  _.isArguments = function(obj) {

    return toString.call(obj) == '[object Arguments]';

  };

  if (!_.isArguments(arguments)) {

    _.isArguments = function(obj) {

      return !!(obj && hasOwnProperty.call(obj, 'callee'));

    };

  }

  // Is a given value a function?

  _.isFunction = function(obj) {

    return toString.call(obj) == '[object Function]';

  };

  // Is a given value a string?

  _.isString = function(obj) {

    return toString.call(obj) == '[object String]';

  };

  // Is a given value a number?

  _.isNumber = function(obj) {

    return toString.call(obj) == '[object Number]';

  };

  // Is the given value `NaN`?

  _.isNaN = function(obj) {

    // `NaN` is the only value for which `===` is not reflexive.

    return obj !== obj;

  };

  // Is a given value a boolean?

  _.isBoolean = function(obj) {

    return obj === true || obj === false || toString.call(obj) == '[object Boolean]';

  };

  // Is a given value a date?

  _.isDate = function(obj) {

    return toString.call(obj) == '[object Date]';

  };