/files/underscorejs/1.4.2/underscore.js

//     Underscore.js 1.4.2

//     http://underscorejs.org

//     (c) 2009-2012 Jeremy Ashkenas, DocumentCloud Inc.

//     Underscore may be freely distributed under the MIT license.



(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 push             = ArrayProto.push,

      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) {

    if (obj instanceof _) return obj;

    if (!(this instanceof _)) return new _(obj);

    this._wrapped = obj;

  };



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

  // backwards-compatibility for the old `require()` API. If we're in

  // the browser, add `_` as a global object via a string identifier,

  // for Closure Compiler "advanced" mode.

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

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

      exports = module.exports = _;

    }

    exports._ = _;

  } else {

    root['_'] = _;

  }



  // Current version.

  _.VERSION = '1.4.2';



  // 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 (iterator.call(context, obj[i], i, obj) === breaker) return;

      }

    } else {

      for (var key in obj) {

        if (_.has(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 = _.collect = 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 arguments.length > 2 ? obj.reduceRight(iterator, memo) : obj.reduceRight(iterator);

    }

    var length = obj.length;

    if (length !== +length) {

      var keys = _.keys(obj);

      length = keys.length;

    }

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

      index = keys ? keys[--length] : --length;

      if (!initial) {

        memo = obj[index];

        initial = true;

      } else {

        memo = iterator.call(context, memo, obj[index], index, list);

      }

    });

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

    return memo;

  };



  // 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) {

    iterator || (iterator = _.identity);

    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 the array or object contains a given value (using `===`).

  // Aliased as `include`.

  _.contains = _.include = 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 (_.isFunction(method) ? method : 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]; });

  };



  // Convenience version of a common use case of `filter`: selecting only objects

  // with specific `key:value` pairs.

  _.where = function(obj, attrs) {

    if (_.isEmpty(attrs)) return [];

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

      for (var key in attrs) {

        if (attrs[key] !== value[key]) return false;

      }

      return true;

    });

  };



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

  // Can't optimize arrays of integers longer than 65,535 elements.

  // See: https://bugs.webkit.org/show_bug.cgi?id=80797

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

    if (!iterator && _.isArray(obj) && obj[0] === +obj[0] && obj.length < 65535) {

      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) && obj[0] === +obj[0] && obj.length < 65535) {

      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 rand;

    var index = 0;

    var shuffled = [];

    each(obj, function(value) {

      rand = _.random(index++);

      shuffled[index - 1] = shuffled[rand];

      shuffled[rand] = value;

    });

    return shuffled;

  };



  // An internal function to generate lookup iterators.

  var lookupIterator = function(value) {

    return _.isFunction(value) ? value : function(obj){ return obj[value]; };

  };



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

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

    var iterator = lookupIterator(value);

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

      return {

        value : value,

        index : index,

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

      };

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

      var a = left.criteria;

      var b = right.criteria;

      if (a !== b) {

        if (a > b || a === void 0) return 1;

        if (a < b || b === void 0) return -1;

      }

      return left.index < right.index ? -1 : 1;

    }), 'value');

  };



  // An internal function used for aggregate "group by" operations.

  var group = function(obj, value, context, behavior) {

    var result = {};

    var iterator = lookupIterator(value);

    each(obj, function(value, index) {

      var key = iterator.call(context, value, index, obj);

      behavior(result, key, value);

    });

    return result;

  };



  // 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, value, context) {

    return group(obj, value, context, function(result, key, value) {

      (_.has(result, key) ? result[key] : (result[key] = [])).push(value);

    });

  };



  // Counts instances of an object that group by a certain criterion. Pass

  // either a string attribute to count by, or a function that returns the

  // criterion.

  _.countBy = function(obj, value, context) {

    return group(obj, value, context, function(result, key, value) {

      if (!_.has(result, key)) result[key] = 0;

      result[key]++;

    });

  };



  // Use a comparator function to figure out the smallest index at which

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

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

    iterator = iterator == null ? _.identity : lookupIterator(iterator);

    var value = iterator.call(context, obj);

    var low = 0, high = array.length;

    while (low < high) {

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

      iterator.call(context, array[mid]) < value ? low = mid + 1 : high = mid;

    }

    return low;

  };



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

  _.toArray = function(obj) {

    if (!obj) return [];

    if (obj.length === +obj.length) return slice.call(obj);

    return _.values(obj);

  };



  // Return the number of elements in an object.

  _.size = function(obj) {

    return (obj.length === +obj.length) ? obj.length : _.keys(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` and `take`. The **guard** check

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

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

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

  };



  // Returns everything but the last entry of the array. Especially 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` and `drop`.

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

  // the rest N values in the array. The **guard**

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

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

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

  };



  // Trim out all falsy values from an array.

  _.compact = function(array) {

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

  };



  // Internal implementation of a recursive `flatten` function.

  var flatten = function(input, shallow, output) {

    each(input, function(value) {

      if (_.isArray(value)) {

        shallow ? push.apply(output, value) : flatten(value, shallow, output);

      } else {

        output.push(value);

      }

    });

    return output;

  };



  // Return a completely flattened version of an array.

  _.flatten = function(array, shallow) {

    return flatten(array, shallow, []);

  };



  // 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, context) {

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

    var results = [];

    var seen = [];

    each(initial, function(value, index) {

      if (isSorted ? (!index || seen[seen.length - 1] !== value) : !_.contains(seen, value)) {

        seen.push(value);

        results.push(array[index]);

      }

    });

    return results;

  };



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

  // the passed-in arrays.

  _.union = function() {

    return _.uniq(concat.apply(ArrayProto, arguments));

  };



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

  // passed-in arrays.

  _.intersection = 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 = concat.apply(ArrayProto, slice.call(arguments, 1));

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

  };



  // Converts lists into objects. Pass either a single array of `[key, value]`

  // pairs, or two parallel arrays of the same length -- one of keys, and one of

  // the corresponding values.

  _.object = function(list, values) {

    var result = {};

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

      if (values) {

        result[list[i]] = values[i];

      } else {

        result[list[i][0]] = list[i][1];

      }

    }

    return result;

  };



  // 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 = 0, l = array.length;

    if (isSorted) {

      if (typeof isSorted == 'number') {

        i = (isSorted < 0 ? Math.max(0, l + isSorted) : isSorted);

      } else {

        i = _.sortedIndex(array, item);

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

      }

    }

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

    for (; i < l; i++) if (array[i] === item) return i;

    return -1;

  };



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

  _.lastIndexOf = function(array, item, from) {

    if (array == null) return -1;

    var hasIndex = from != null;

    if (nativeLastIndexOf && array.lastIndexOf === nativeLastIndexOf) {

      return hasIndex ? array.lastIndexOf(item, from) : array.lastIndexOf(item);

    }

    var i = (hasIndex ? from : array.length);

    while (i--) if (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 _.has(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(null, 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, result;

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

    return function() {

      context = this; args = arguments;

      var later = function() {

        timeout = null;

        if (more) {

          result = func.apply(context, args);

        }

        whenDone();

      };

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

      if (throttling) {

        more = true;

      } else {

        throttling = true;

        result = func.apply(context, args);

      }

      whenDone();

      return result;

    };

  };



  // 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. If `immediate` is passed, trigger the function on the

  // leading edge, instead of the trailing.

  _.debounce = function(func, wait, immediate) {

    var timeout, result;

    return function() {

      var context = this, args = arguments;

      var later = function() {

        timeout = null;

        if (!immediate) result = func.apply(context, args);

      };

      var callNow = immediate && !timeout;

      clearTimeout(timeout);

      timeout = setTimeout(later, wait);

      if (callNow) result = func.apply(context, args);

      return result;

    };

  };



  // 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;

      memo = func.apply(this, arguments);

      func = null;

      return memo;

    };

  };



  // 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 = [func];

      push.apply(args, 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 (_.has(obj, key)) keys[keys.length] = key;

    return keys;

  };



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

  _.values = function(obj) {

    var values = [];

    for (var key in obj) if (_.has(obj, key)) values.push(obj[key]);

    return values;

  };



  // Convert an object into a list of `[key, value]` pairs.

  _.pairs = function(obj) {

    var pairs = [];

    for (var key in obj) if (_.has(obj, key)) pairs.push([key, obj[key]]);

    return pairs;

  };



  // Invert the keys and values of an object. The values must be serializable.

  _.invert = function(obj) {

    var result = {};

    for (var key in obj) if (_.has(obj, key)) result[obj[key]] = key;

    return result;

  };



  // 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) {

        obj[prop] = source[prop];

      }

    });

    return obj;

  };



  // Return a copy of the object only containing the whitelisted properties.

  _.pick = function(obj) {

    var copy = {};

    var keys = concat.apply(ArrayProto, slice.call(arguments, 1));

    each(keys, function(key) {

      if (key in obj) copy[key] = obj[key];

    });

    return copy;

  };



   // Return a copy of the object without the blacklisted properties.

  _.omit = function(obj) {

    var copy = {};

    var keys = concat.apply(ArrayProto, slice.call(arguments, 1));

    for (var key in obj) {

      if (!_.contains(keys, key)) copy[key] = obj[key];

    }

    return copy;

  };



  // 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 for `isEqual`.

  var eq = function(a, b, aStack, bStack) {

    // 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 instanceof _) a = a._wrapped;

    if (b instanceof _) b = b._wrapped;

    // 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 = aStack.length;

    while (length--) {

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

      // unique nested structures.

      if (aStack[length] == a) return bStack[length] == b;

    }

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

    aStack.push(a);

    bStack.push(b);

    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--) {

          if (!(result = eq(a[size], b[size], aStack, bStack))) break;

        }

      }

    } else {

      // Objects with different constructors are not equivalent, but `Object`s

      // from different frames are.

      var aCtor = a.constructor, bCtor = b.constructor;

      if (aCtor !== bCtor && !(_.isFunction(aCtor) && (aCtor instanceof aCtor) &&

                               _.isFunction(bCtor) && (bCtor instanceof bCtor))) {

        return false;

      }

      // Deep compare objects.

      for (var key in a) {

        if (_.has(a, key)) {

          // Count the expected number of properties.

          size++;

          // Deep compare each member.

          if (!(result = _.has(b, key) && eq(a[key], b[key], aStack, bStack))) break;

        }

      }

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

      if (result) {

        for (key in b) {

          if (_.has(b, key) && !(size--)) break;

        }

        result = !size;

      }

    }

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

    aStack.pop();

    bStack.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 (obj == null) return true;

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

    for (var key in obj) if (_.has(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);

  };



  // Add some isType methods: isArguments, isFunction, isString, isNumber, isDate, isRegExp.

  each(['Arguments', 'Function', 'String', 'Number', 'Date', 'RegExp'], function(name) {

    _['is' + name] = function(obj) {

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

    };

  });



  // Define a fallback version of the method in browsers (ahem, IE), where

  // there isn't any inspectable "Arguments" type.

  if (!_.isArguments(arguments)) {

    _.isArguments = function(obj) {

      return !!(obj && _.has(obj, 'callee'));

    };

  }



  // Optimize `isFunction` if appropriate.

  if (typeof (/./) !== 'function') {

    _.isFunction = function(obj) {

      return typeof obj === 'function';

    };

  }



  // Is a given object a finite number?

  _.isFinite = function(obj) {

    return _.isNumber(obj) && isFinite(obj);

  };



  // Is the given value `NaN`? (NaN is the only number which does not equal itself).

  _.isNaN = function(obj) {

    return _.isNumber(obj) && 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 equal to null?

  _.isNull = function(obj) {

    return obj === null;

  };



  // Is a given variable undefined?

  _.isUndefined = function(obj) {

    return obj === void 0;

  };



  // Shortcut function for checking if an object has a given property directly

  // on itself (in other words, not on a prototype).

  _.has = function(obj, key) {

    return hasOwnProperty.call(obj, key);

  };



  // Utility Functions

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



  // Run Underscore.js in *noConflict* mode, returning the `_` variable to its

  // previous owner. Returns a reference to the Underscore object.

  _.noConflict = function() {

    root._ = previousUnderscore;

    return this;

  };



  // Keep the identity function around for default iterators.

  _.identity = function(value) {

    return value;

  };



  // Run a function **n** times.

  _.times = function(n, iterator, context) {

    for (var i = 0; i < n; i++) iterator.call(context, i);

  };



  // Return a random integer between min and max (inclusive).

  _.random = function(min, max) {

    if (max == null) {

      max = min;

      min = 0;

    }

    return min + (0 | Math.random() * (max - min + 1));

  };



  // List of HTML entities for escaping.

  var entityMap = {

    escape: {

      '&': '&amp;',

      '<': '&lt;',

      '>': '&gt;',

      '"': '&quot;',

      "'": '&#x27;',

      '/': '&#x2F;'

    }

  };

  entityMap.unescape = _.invert(entityMap.escape);



  // Regexes containing the keys and values listed immediately above.

  var entityRegexes = {

    escape:   new RegExp('[' + _.keys(entityMap.escape).join('') + ']', 'g'),

    unescape: new RegExp('(' + _.keys(entityMap.unescape).join('|') + ')', 'g')

  };



  // Functions for escaping and unescaping strings to/from HTML interpolation.

  _.each(['escape', 'unescape'], function(method) {

    _[method] = function(string) {

      if (string == null) return '';

      return ('' + string).replace(entityRegexes[method], function(match) {

        return entityMap[method][match];

      });

    };

  });



  // If the value of the named property is a function then invoke it;

  // otherwise, return it.

  _.result = function(object, property) {

    if (object == null) return null;

    var value = object[property];

    return _.isFunction(value) ? value.call(object) : value;

  };



  // Add your own custom functions to the Underscore object.

  _.mixin = function(obj) {

    each(_.functions(obj), function(name){

      var func = _[name] = obj[name];

      _.prototype[name] = function() {

        var args = [this._wrapped];

        push.apply(args, arguments);

        return result.call(this, func.apply(_, args));

      };

    });

  };



  // Generate a unique integer id (unique within the entire client session).

  // Useful for temporary DOM ids.

  var idCounter = 0;

  _.uniqueId = function(prefix) {

    var id = idCounter++;

    return prefix ? prefix + id : id;

  };



  // By default, Underscore uses ERB-style template delimiters, change the

  // following template settings to use alternative delimiters.

  _.templateSettings = {

    evaluate    : /<%([\s\S]+?)%>/g,

    interpolate : /<%=([\s\S]+?)%>/g,

    escape      : /<%-([\s\S]+?)%>/g

  };



  // When customizing `templateSettings`, if you don't want to define an

  // interpolation, evaluation or escaping regex, we need one that is

  // guaranteed not to match.

  var noMatch = /(.)^/;



  // Certain characters need to be escaped so that they can be put into a

  // string literal.

  var escapes = {

    "'":      "'",

    '\\':     '\\',

    '\r':     'r',

    '\n':     'n',

    '\t':     't',

    '\u2028': 'u2028',

    '\u2029': 'u2029'

  };



  var escaper = /\\|'|\r|\n|\t|\u2028|\u2029/g;



  // JavaScript micro-templating, similar to John Resig's implementation.

  // Underscore templating handles arbitrary delimiters, preserves whitespace,

  // and correctly escapes quotes within interpolated code.

  _.template = function(text, data, settings) {

    settings = _.defaults({}, settings, _.templateSettings);



    // Combine delimiters into one regular expression via alternation.

    var matcher = new RegExp([

      (settings.escape || noMatch).source,

      (settings.interpolate || noMatch).source,

      (settings.evaluate || noMatch).source

    ].join('|') + '|$', 'g');



    // Compile the template source, escaping string literals appropriately.

    var index = 0;

    var source = "__p+='";

    text.replace(matcher, function(match, escape, interpolate, evaluate, offset) {

      source += text.slice(index, offset)

        .replace(escaper, function(match) { return '\\' + escapes[match]; });

      source +=

        escape ? "'+\n((__t=(" + escape + "))==null?'':_.escape(__t))+\n'" :

        interpolate ? "'+\n((__t=(" + interpolate + "))==null?'':__t)+\n'" :

        evaluate ? "';\n" + evaluate + "\n__p+='" : '';

      index = offset + match.length;

    });

    source += "';\n";



    // If a variable is not specified, place data values in local scope.

    if (!settings.variable) source = 'with(obj||{}){\n' + source + '}\n';



    source = "var __t,__p='',__j=Array.prototype.join," +

      "print=function(){__p+=__j.call(arguments,'');};\n" +

      source + "return __p;\n";



    try {

      var render = new Function(settings.variable || 'obj', '_', source);

    } catch (e) {

      e.source = source;

      throw e;

    }



    if (data) return render(data, _);

    var template = function(data) {

      return render.call(this, data, _);

    };



    // Provide the compiled function source as a convenience for precompilation.

    template.source = 'function(' + (settings.variable || 'obj') + '){\n' + source + '}';



    return template;

  };



  // Add a "chain" function, which will delegate to the wrapper.

  _.chain = function(obj) {

    return _(obj).chain();

  };



  // OOP

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

  // If Underscore is called as a function, it returns a wrapped object that

  // can be used OO-style. This wrapper holds altered versions of all the

  // underscore functions. Wrapped objects may be chained.



  // Helper function to continue chaining intermediate results.

  var result = function(obj) {

    return this._chain ? _(obj).chain() : obj;

  };



  // Add all of the Underscore functions to the wrapper object.

  _.mixin(_);



  // Add all mutator Array functions to the wrapper.

  each(['pop', 'push', 'reverse', 'shift', 'sort', 'splice', 'unshift'], function(name) {

    var method = ArrayProto[name];

    _.prototype[name] = function() {

      var obj = this._wrapped;

      method.apply(obj, arguments);

      if ((name == 'shift' || name == 'splice') && obj.length === 0) delete obj[0];

      return result.call(this, obj);

    };

  });



  // Add all accessor Array functions to the wrapper.

  each(['concat', 'join', 'slice'], function(name) {

    var method = ArrayProto[name];

    _.prototype[name] = function() {

      return result.call(this, method.apply(this._wrapped, arguments));

    };

  });



  _.extend(_.prototype, {



    // Start chaining a wrapped Underscore object.

    chain: function() {

      this._chain = true;

      return this;

    },



    // Extracts the result from a wrapped and chained object.

    value: function() {

      return this._wrapped;

    }



  });



}).call(this);