lodash/lodash.js

/*!
 * Lo-Dash v0.1.0 <https://github.com/bestiejs/lodash>
 * Copyright 2012 John-David Dalton <http://allyoucanleet.com/>
 * Based on Underscore.js 1.3.3, copyright 2009-2012 Jeremy Ashkenas, DocumentCloud Inc.
 * <http://documentcloud.github.com/underscore>
 * Available under MIT license <http://mths.be/mit>
 */
;(function(window, undefined) {
  'use strict';

  /** Used to escape and unescape characters in templates */
  var escapes = {
    '\\': '\\',
    "'": "'",
    'r': '\r',
    'n': '\n',
    't': '\t',
    'u2028': '\u2028',
    'u2029': '\u2029'
  };

  // assign the result as keys and the keys as values
  (function() {
    for (var prop in escapes) {
      escapes[escapes[prop]] = prop;
    }
  }());

  /** Detect free variable `exports` */
  var freeExports = typeof exports == 'object' && exports &&
    (typeof global == 'object' && global && global == global.global && (window = global), exports);

  /** Used to generate unique IDs */
  var idCounter = 0;

  /** Used to restore the original `_` reference in `noConflict` */
  var oldDash = window._;

  /** Used to replace unescape characters with their escaped counterpart */
  var reEscaper = /\\|'|\r|\n|\t|\u2028|\u2029/g;

  /**
   * Used for `templateSettings` properties such as `escape`, `evaluate`,
   * or `interpolate` with explicitly assigned falsey values to ensure no match
   * is made.
   */
  var reNoMatch = /.^/;

  /** Used to replace escaped characters with their unescaped counterpart */
  var reUnescaper = /\\(\\|'|r|n|t|u2028|u2029)/g;

  /** Object#toString result shortcuts */
  var arrayClass = '[object Array]',
      boolClass = '[object Boolean]',
      dateClass = '[object Date]',
      funcClass = '[object Function]',
      numberClass = '[object Number]',
      regexpClass = '[object RegExp]',
      stringClass = '[object String]';

  /** Native prototype shortcuts */
  var ArrayProto = Array.prototype,
      ObjProto = Object.prototype;

  /** Native method shortcuts */
  var concat = ArrayProto.concat,
      hasOwnProperty = ObjProto.hasOwnProperty,
      push = ArrayProto.push,
      slice = ArrayProto.slice,
      toString = ObjProto.toString,
      unshift = ArrayProto.unshift;

  /* Native method shortcuts for methods with the same name as a `lodash` method */
  var nativeIsArray = Array.isArray,
      nativeIsFinite = window.isFinite,
      nativeKeys = Object.keys;

  /** Timer shortcuts */
  var clearInteval = window.clearInterval,
      setTimeout = window.setTimeout;

  /** Compilation options for `_.difference` */
  var differenceFactoryOptions = {
    'args': 'array',
    'top': 'var values=concat.apply([],slice.call(arguments,1))',
    'init': '[]',
    'inLoop': 'indexOf(values,array[index])<0&&result.push(array[index])'
  };

  /** Compilation options for `_.every` */
  var everyFactoryOptions = {
    'init': 'true',
    'inLoop': 'if(!callback(collection[index],index,collection))return !result'
  };

  /** Compilation options for `_.extend` */
  var extendFactoryOptions = {
    'args': 'object',
    'init': 'object',
    'beforeLoop': 'for(var source,j=1,length=arguments.length;j<length;j++){\nsource=arguments[j]',
    'loopExp': 'index in source',
    'inLoop': 'object[index]=source[index]',
    'useHas': false,
    'afterLoop': '}'
  };

  /** Compilation options for `_.filter` */
  var filterFactoryOptions = {
    'init': '[]',
    'inLoop': 'callback(collection[index],index,collection)&&result.push(collection[index])'
  };

  /** Compilation options for `_.forEach` */
  var forEachFactoryOptions = {
    'args': 'collection,callback,thisArg',
    'top': 'if(!callback){\ncallback=identity\n}\nelse if(thisArg){\ncallback=bind(callback,thisArg)\n}',
    'init': 'collection',
    'inLoop': 'callback(collection[index],index,collection)'
  };

  /** Compilation options for `_.keys` */
  var keysFactoryOptions = {
    'args': 'object',
    'top': 'if(object!==Object(object))throw TypeError()',
    'init': '[]',
    'inLoop': 'result.push(index)'
  };

  /** Compilation options for `_.map` */
  var mapFactoryOptions = {
    'init': '',
    'exits': '[]',
    'beforeLoop': {
      'array': 'result=Array(length)',
      'object': 'result=[]'
    },
    'inLoop': {
      'array': 'result[index]=callback(collection[index],index,collection)',
      'object': 'result[result.length]=callback(collection[index],index,collection)'
    }
  };

  /** Compilation options for `_.max` */
  var maxFactoryOptions = {
    'top':
      'var current,result=-Infinity,computed=result;\n' +
      'if(!callback){\n' +
      'if(isArray(collection)&&collection[0]===+collection[0])return Math.max.apply(Math,collection);\n' +
      'if(isEmpty(collection))return result;\n' +
      '}else if(thisArg)callback=bind(callback,thisArg)',
    'inLoop':
        'current=callback?callback(collection[index],index,collection):collection[index];\n' +
        'if(current>=computed)computed=current,result=collection[index]'
  };

  /*--------------------------------------------------------------------------*/

  /**
   * The `lodash` function.
   *
   * @name _
   * @param {Mixed} value The value to wrap in a `Lodash` instance.
   * @returns {Object} Returns a `Lodash` instance.
   */
  function lodash(value) {
    // allow invoking `lodash` without the `new` operator
    return new Lodash(value);
  }

  /**
   * Creates a `Lodash` instance that wraps a value to allow chaining.
   *
   * @private
   * @constructor
   * @param {Mixed} value The value to wrap.
   */
  function Lodash(value) {
    this._wrapped = value;
  }

  /*--------------------------------------------------------------------------*/

  /**
   * Checks if a `value` is an array.
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Mixed} value The value to check.
   * @returns {Boolean} Returns `true` if the `value` is an array, else `false`.
   * @example
   *
   * (function() { return _.isArray(arguments); })();
   * // => false
   *
   * _.isArray([1, 2, 3]);
   * // => true
   */
  var isArray = nativeIsArray || function isArray(value) {
    return toString.call(value) == arrayClass;
  };

  /**
   * Checks if a `value` is empty. Arrays or strings with a length of 0 and
   * objects with no enumerable own properties are considered "empty".
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Mixed} value The value to check.
   * @returns {Boolean} Returns `true` if the `value` is empty, else `false`.
   * @example
   *
   * _.isEmpty([1, 2, 3]);
   * // => false
   *
   * _.isEmpty({});
   * // => true
   */
  var isEmpty = iterationFactory({
    'args': 'value',
    'iterate': 'objects',
    'top': 'var className=toString.call(value)',
    'init': 'true',
    'beforeLoop': 'if(className==arrayClass||className==stringClass)return !value.length',
    'inLoop': 'return false'
  });

  /*--------------------------------------------------------------------------*/

  /**
   * Compiles iteration functions.
   *
   * @private
   * @param {Object} [options1, options2, ..] The compile options objects.
   * @returns {Function} Returns the compiled function.
   */
  function iterationFactory() {
    var prop,
        index = -1,
        array = {},
        object = {},
        options = {},
        props = ['beforeLoop', 'loopExp', 'inLoop', 'afterLoop'];

    while (++index < arguments.length) {
      for (prop in arguments[index]) {
        options[prop] = arguments[index][prop];
      }
    }

    while ((prop = props.pop())) {
      if (typeof options[prop] == 'object') {
        array[prop] = options[prop].array;
        object[prop] = options[prop].object;
      } else {
        array[prop] = object[prop] = options[prop] || '';
      }
    }

    var args = options.args,
        firstArg = /^[^,]+/.exec(args)[0],
        init = options.init,
        iterate = options.iterate,
        arrayBranch = !(args == 'object' || iterate == 'objects'),
        objectBranch = !(args == 'array' || iterate == 'arrays'),
        useHas = options.useHas !== false;

    return Function('arrayClass,bind,concat,funcClass,hasOwnProperty,identity,' +
                    'indexOf,Infinity,isArray,isEmpty,Math,slice,stringClass,'+
                    'toString,undefined',
      '"use strict";' +
      'return function(' + args + '){\n' +
        (options.top || '') + ';\n' +
        ('var index, result' + (init ? '=' + init : '')) + ';\n' +
        'if(' + firstArg + '==undefined)return ' + (options.exits || 'result') + ';\n' +
        (arrayBranch
          ? 'var length=' + firstArg + '.length;\nindex=-1;\n' +
            ((objectBranch ? 'if(length===+length){\n'  : '') +
            (array.beforeLoop || '') + ';\n' +
            'while(' + (array.loopExp || '++index<length') + '){\n' + array.inLoop + '\n}' +
            (array.afterLoop || '') + ';\n' +
            (objectBranch ? '\n}\n' : ''))
          : ''
        ) +
        (objectBranch
          ? ((arrayBranch ? 'else{\n' : '') +
            (object.beforeLoop || '') + ';\n' +
            'for(' + (object.loopExp || 'index in ' + firstArg) + '){\n' +
              (useHas ? 'if(hasOwnProperty.call(' + /\S+$/.exec(object.loopExp || firstArg)[0] + ',index)){\n' : '') +
                object.inLoop +
              (useHas ? '\n}' : '') +
            '\n}' +
            (object.afterLoop || '') + ';\n' +
            (arrayBranch ? '\n}\n' : ''))
          : ''
        ) +
        (options.bottom || '') + ';\n' +
        'return ' + (options.returns || 'result') +
      '\n}'
    )(arrayClass, bind, concat, funcClass, hasOwnProperty, identity,
      indexOf, Infinity, isArray, isEmpty, Math, slice, stringClass, toString);
  }

  /**
   * Unescapes characters, previously escaped for inclusion in compiled string
   * literals, so they may compiled into function bodies.
   * (Used for template interpolation, evaluation, or escaping)
   *
   * @private
   * @param {String} string The string to unescape.
   * @returns {String} Returns the unescaped string.
   */
  function unescape(string) {
    return string.replace(reUnescaper, function(match, escaped) {
      return escapes[escaped];
    });
  }

  /*--------------------------------------------------------------------------*/

  /**
   * Checks if a given `target` value is present in a `collection` using strict
   * equality for comparisons, i.e. `===`.
   *
   * @static
   * @memberOf _
   * @alias include
   * @category Collections
   * @param {Array|Object} collection The collection to iterate over.
   * @param {Mixed} target The value to check for.
   * @returns {Boolean} Returns `true` if `target` value is found, else `false`.
   * @example
   *
   * _.contains([1, 2, 3], 3);
   * // => true
   */
  var contains = iterationFactory({
    'args': 'collection,target',
    'init': 'false',
    'inLoop': 'if(collection[index]===target)return true'
  });

  /**
   * Checks if the `callback` returns truthy for **all** values of a `collection`.
   * The `callback` is invoked with 3 arguments; for arrays they are
   * (value, index, array) and for objects they are (value, key, object).
   *
   * @static
   * @memberOf _
   * @alias all
   * @category Collections
   * @param {Array|Object} collection The collection to iterate over.
   * @param {Function} callback The function called per iteration.
   * @param {Mixed} [thisArg] The `this` binding for the callback.
   * @returns {Boolean} Returns `true` if all values pass the callback check, else `false`.
   * @example
   *
   * _.every([true, 1, null, 'yes'], Boolean);
   * => false
   */
  var every = iterationFactory(forEachFactoryOptions, everyFactoryOptions);

  /**
   * Examines each value in a `collection`, returning an array of all values the
   * `callback` returns truthy for. The `callback` is invoked with 3 arguments;
   * for arrays they are (value, index, array) and for objects they are
   * (value, key, object).
   *
   * @static
   * @memberOf _
   * @alias select
   * @category Collections
   * @param {Array|Object} collection The collection to iterate over.
   * @param {Function} callback The function called per iteration.
   * @param {Mixed} [thisArg] The `this` binding for the callback.
   * @returns {Array} Returns a new array of values that passed callback check.
   * @example
   *
   * var evens = _.filter([1, 2, 3, 4, 5, 6], function(num) { return num % 2 == 0; });
   * // => [2, 4, 6]
   */
  var filter = iterationFactory(forEachFactoryOptions, filterFactoryOptions);

  /**
   * Examines each value in a `collection`, returning the first one the `callback`
   * returns truthy for. The function returns as soon as it finds an acceptable
   * value, and does not iterate over the entire `collection`. The `callback` is
   * invoked with 3 arguments; for arrays they are (value, index, array) and for
   * objects they are (value, key, object).
   *
   * @static
   * @memberOf _
   * @alias detect
   * @category Collections
   * @param {Array|Object} collection The collection to iterate over.
   * @param {Function} callback The function called per iteration.
   * @param {Mixed} [thisArg] The `this` binding for the callback.
   * @returns {Mixed} Returns the value that passed the callback check, else `undefined`.
   * @example
   *
   * var even = _.find([1, 2, 3, 4, 5, 6], function(num) { return num % 2 == 0; });
   * // => 2
   */
  var find = iterationFactory(forEachFactoryOptions, {
    'inLoop': 'if(callback(collection[index],index,collection))return collection[index]'
  });

  /**
   * Iterates over a `collection`, executing the `callback` for each value in the
   * `collection`. The `callback` is bound to the `thisArg` value, if one is passed.
   * The `callback` is invoked with 3 arguments; for arrays they are
   * (value, index, array) and for objects they are (value, key, object).
   *
   * @static
   * @memberOf _
   * @alias each
   * @category Collections
   * @param {Array|Object} collection The collection to iterate over.
   * @param {Function} callback The function called per iteration.
   * @param {Mixed} [thisArg] The `this` binding for the callback.
   * @returns {Array|Object} Returns the `collection`.
   * @example
   *
   * _.forEach([1, 2, 3], function(num) { alert(num); });
   * // => alerts each number in turn...
   *
   * _.forEach({ 'one': 1, 'two': 2, 'three': 3}, function(num) { alert(num); });
   * // => alerts each number in turn...
   */
  var forEach = iterationFactory(forEachFactoryOptions);

  /**
   * Splits a `collection` into sets, grouped by the result of running each value
   * through `callback`. The `callback` is invoked with 3 arguments; for arrays
   * they are (value, index, array) and for objects they are (value, key, object).
   * The `callback` argument may also be the name of a property to group by.
   *
   * @static
   * @memberOf _
   * @category Collections
   * @param {Array|Object} collection The collection to iterate over.
   * @param {Function|String} callback The function called per iteration or
   *  property name to group by.
   * @param {Mixed} [thisArg] The `this` binding for the callback.
   * @returns {Object} Returns an object of grouped values.
   * @example
   *
   * _.groupBy([1.3, 2.1, 2.4], function(num) { return Math.floor(num); });
   * // => { '1': [1.3], '2': [2.1, 2.4] }
   *
   * _.groupBy(['one', 'two', 'three'], 'length');
   * // => { '3': ['one', 'two'], '5': ['three'] }
   */
  function groupBy(collection, callback, thisArg) {
    var result = {};
    if (!isFunction(callback)) {
      var prop = callback;
      callback = function(collection) { return collection[prop]; };
    }
    forEach(collection, function(value, index, collection) {
      var prop = callback(value, index, collection);
      (result[prop] || (result[prop] = [])).push(value);
    });
    return result;
  }

  /**
   * Calls the method named by `methodName` for each value of the `collection`.
   * Additional arguments will be passed to each invoked method.
   *
   * @static
   * @memberOf _
   * @category Collections
   * @param {Array|Object} collection The collection to iterate over.
   * @param {String} methodName The name of the method to invoke.
   * @param {Mixed} [arg1, arg2, ...] Arguments to invoke the method with.
   * @returns {Array} Returns a new array of values returned from each invoked method.
   * @example
   *
   * _.invoke([[5, 1, 7], [3, 2, 1]], 'sort');
   * // => [[1, 5, 7], [1, 2, 3]]
   */
  function invoke(collection, methodName) {
    var args = slice.call(arguments, 2),
        isFunc = isFunction(methodName);

    return map(collection, function(value) {
      return (isFunc ? methodName || value : value[methodName]).apply(value, args);
    });
  }

  /**
   * Produces a new array of values by mapping each value in the `collection`
   * through a transformation `callback`. The `callback` is bound to the `thisArg`
   * value, if one is passed. The `callback` is invoked with 3 arguments; for
   * arrays they are (value, index, array) and for objects they are (value, key, object).
   *
   * @static
   * @memberOf _
   * @alias collect
   * @category Collections
   * @param {Array|Object} collection The collection to iterate over.
   * @param {Function} callback The function called per iteration.
   * @param {Mixed} [thisArg] The `this` binding for the callback.
   * @returns {Array} Returns a new array of values returned by the callback.
   * @example
   *
   * _.map([1, 2, 3], function(num) { return num * 3; });
   * // => [3, 6, 9]
   *
   * _.map({ 'one': 1, 'two': 2, 'three': 3 }, function(num) { return num * 3; });
   * // => [3, 6, 9]
   */
  var map = iterationFactory(forEachFactoryOptions, mapFactoryOptions);

  /**
   * Retrieves the maximum value of a `collection`. If `callback` is passed,
   * it will be executed for each value in the `collection` to generate the
   * criterion by which the value is ranked. The `callback` is invoked with 3
   * arguments; for arrays they are (value, index, array) and for objects they
   * are (value, key, object).
   *
   * @static
   * @memberOf _
   * @category Collections
   * @param {Array|Object} collection The collection to iterate over.
   * @param {Function} [callback] The function called per iteration.
   * @param {Mixed} [thisArg] The `this` binding for the callback.
   * @returns {Mixed} Returns the maximum value.
   * @example
   *
   * var stooges = [
   *   { 'name': 'moe', 'age': 40 },
   *   { 'name': 'larry', 'age': 50 },
   *   { 'name': 'curly', 'age': 60 }
   * ];
   *
   * _.max(stooges, function(stooge) { return stooge.age; });
   * // => { 'name': 'curly', 'age': 60 };
   */
  var max = iterationFactory(forEachFactoryOptions, maxFactoryOptions);

  /**
   * Retrieves the minimum value of a `collection`. If `callback` is passed,
   * it will be executed for each value in the `collection` to generate the
   * criterion by which the value is ranked. The `callback` is invoked with 3
   * arguments; for arrays they are (value, index, array) and for objects they
   * are (value, key, object).
   *
   * @static
   * @memberOf _
   * @category Collections
   * @param {Array|Object} collection The collection to iterate over.
   * @param {Function} [callback] The function called per iteration.
   * @param {Mixed} [thisArg] The `this` binding for the callback.
   * @returns {Mixed} Returns the minimum value.
   * @example
   *
   * _.min([10, 5, 100, 2, 1000]);
   * // => 2
   */
  var min = iterationFactory(forEachFactoryOptions, maxFactoryOptions, {
    'top': maxFactoryOptions.top.replace('-', '').replace('max', 'min'),
    'inLoop': maxFactoryOptions.inLoop.replace('>=', '<')
  });

  /**
   * Retrieves the value of a specified property from all values in a `collection`.
   *
   * @static
   * @memberOf _
   * @category Collections
   * @param {Array|Object} collection The collection to iterate over.
   * @param {String} property The property to pluck.
   * @returns {Array} Returns a new array of property values.
   * @example
   *
   * var stooges = [
   *   { 'name': 'moe', 'age': 40 },
   *   { 'name': 'larry', 'age': 50 },
   *   { 'name': 'curly', 'age': 60 }
   * ];
   *
   * _.pluck(stooges, 'name');
   * // => ['moe', 'larry', 'curly']
   */
  var pluck = iterationFactory(mapFactoryOptions, {
    'args': 'collection,property',
    'inLoop': {
      'array': 'result[index]=collection[index][property]',
      'object': 'result[result.length]=collection[index][property]'
    }
  });

  /**
   * Boils down a `collection` to a single value. The initial state of the
   * reduction is `accumulator` and each successive step of it should be returned
   * by the `callback`. The `callback` is bound to the `thisArg` value, if one is
   * passed. The `callback` is invoked with 4 arguments; for arrays they are
   * (accumulator, value, index, array) and for objects they are
   * (accumulator, value, key, object).
   *
   * @static
   * @memberOf _
   * @alias foldl, inject
   * @category Collections
   * @param {Array|Object} collection The collection to iterate over.
   * @param {Function} callback The function called per iteration.
   * @param {Mixed} [accumulator] Initial value of the accumulator.
   * @param {Mixed} [thisArg] The `this` binding for the callback.
   * @returns {Mixed} Returns the accumulated value.
   * @example
   *
   * var sum = _.reduce([1, 2, 3], function(memo, num) { return memo + num; });
   * // => 6
   */
  var reduce = iterationFactory({
    'args': 'collection,callback,accumulator,thisArg',
    'top': 'var initial=arguments.length>2;\n' + forEachFactoryOptions.top,
    'init': 'accumulator',
    'beforeLoop': {
      'array': 'if(!initial)result=collection[++index]'
    },
    'inLoop': {
      'array': 'result=callback(result,collection[index],index,collection)',
      'object': 'result=initial\n?callback(result,collection[index],index,collection)\n:(initial=true,collection[index])'
    }
  });

  /**
   * The right-associative version of `_.reduce`. The `callback` is bound to the
   * `thisArg` value, if one is passed. The `callback` is invoked with 4 arguments;
   * for arrays they are (accumulator, value, index, array) and for objects they
   * are (accumulator, value, key, object).
   *
   * @static
   * @memberOf _
   * @alias foldr
   * @category Collections
   * @param {Array|Object} collection The collection to iterate over.
   * @param {Function} callback The function called per iteration.
   * @param {Mixed} [accumulator] Initial value of the accumulator.
   * @param {Mixed} [thisArg] The `this` binding for the callback.
   * @returns {Mixed} Returns the accumulated value.
   * @example
   *
   * var list = [[0, 1], [2, 3], [4, 5]];
   * var flat = _.reduceRight(list, function(a, b) { return a.concat(b); }, []);
   * // => [4, 5, 2, 3, 0, 1]
   */
  function reduceRight(collection, callback, result, thisArg) {
    var initial = arguments.length > 2;
    if (collection == undefined) {
      return result;
    }
    if (!callback) {
      callback = identity;
    } else if(thisArg) {
      callback = bind(callback, thisArg);
    }
    var length = collection.length;
    if (length === +length) {
      if (length && !initial) {
        result = collection[--length];
      }
      while (length--) {
        result = callback(result, collection[length], length, collection);
      }
      return result;
    }

    var prop,
        props = keys(collection);

    length = props.length;
    if (length && !initial) {
      result = collection[props[--length]];
    }
    while (length--) {
      prop = props[length];
      result = callback(result, collection[prop], prop, collection);
    }
    return result;
  }

  /**
   * The opposite of `_.filter`, this method returns the values of a `collection`
   * that `callback` does **not** return truthy for. The `callback` is invoked
   * with 3 arguments; for arrays they are (value, index, array) and for objects
   * they are (value, key, object).
   *
   * @static
   * @memberOf _
   * @category Collections
   * @param {Array|Object} collection The collection to iterate over.
   * @param {Function} callback The function called per iteration.
   * @param {Mixed} [thisArg] The `this` binding for the callback.
   * @returns {Array} Returns a new array of values that did **not** pass the callback check.
   * @example
   *
   * var odds = _.reject([1, 2, 3, 4, 5, 6], function(num) { return num % 2 == 0; });
   * // => [1, 3, 5]
   */
  var reject = iterationFactory(forEachFactoryOptions, filterFactoryOptions, {
    'inLoop': '!' + filterFactoryOptions.inLoop
  });

  /**
   * Produces a new array of shuffled `collection` values, using a version of the
   * Fisher-Yates shuffle. See http://en.wikipedia.org/wiki/Fisher-Yates_shuffle.
   *
   * @static
   * @memberOf _
   * @category Collections
   * @param {Array|Object} collection The collection to shuffle.
   * @returns {Array} Returns a new shuffled array.
   * @example
   *
   * _.shuffle([1, 2, 3, 4, 5, 6]);
   * // => [4, 1, 6, 3, 5, 2]
   */
  function shuffle(collection) {
    var rand,
        result = [];

    forEach(collection, function(value, index) {
      rand = Math.floor(Math.random() * (index + 1));
      result[index] = result[rand];
      result[rand] = value;
    });
    return result;
  }

  /**
   * Gets the number of values in the `collection`.
   *
   * @static
   * @memberOf _
   * @category Collections
   * @param {Array|Object} collection The collection inspect.
   * @returns {Number} Returns the number of values in the collection.
   * @example
   *
   * _.size({ 'one': 1, 'two': 2, 'three': 3 });
   * // => 3
   */
  function size(collection) {
    var className = toString.call(collection);
    return className == arrayClass || className == stringClass
      ? collection.length
      : keys(collection).length;
  }

  /**
   * Produces a new sorted array, ranked in ascending order by the results of
   * running each value of a `collection` through `callback`. The `callback` is
   * invoked with 3 arguments; for arrays they are (value, index, array) and for
   * objects they are (value, key, object). The `callback` argument may also be
   * the name of a property to sort by (e.g. 'length').
   *
   * @static
   * @memberOf _
   * @category Collections
   * @param {Array|Object} collection The collection to iterate over.
   * @param {Function|String} callback The function called per iteration or
   *  property name to sort by.
   * @param {Mixed} [thisArg] The `this` binding for the callback.
   * @returns {Array} Returns a new array of sorted values.
   * @example
   *
   * _.sortBy([1, 2, 3, 4, 5, 6], function(num) { return Math.sin(num); });
   * // => [5, 4, 6, 3, 1, 2]
   */
  function sortBy(collection, callback, thisArg) {
    if (!isFunction(callback)) {
      var prop = callback;
      callback = function(collection) { return collection[prop]; };
    } else if (thisArg) {
      callback = bind(callback, thisArg);
    }
    return pluck(map(collection, function(value, index) {
      return {
        'criteria': callback(value, index, collection),
        'value': value
      };
    }).sort(function(left, right) {
      var a = left.criteria,
          b = right.criteria;

      if (a === undefined) {
        return 1;
      }
      if (b === undefined) {
        return -1;
      }
      return a < b ? -1 : a > b ? 1 : 0;
    }), 'value');
  }

  /**
   * Checks if the `callback` returns truthy for **any** value of a `collection`.
   * The function returns as soon as it finds passing value, and does not iterate
   * over the entire `collection`. The `callback` is invoked with 3 arguments; for
   * arrays they are (value, index, array) and for objects they are
   * (value, key, object).
   *
   * @static
   * @memberOf _
   * @alias any
   * @category Collections
   * @param {Array|Object} collection The collection to iterate over.
   * @param {Function} callback The function called per iteration.
   * @param {Mixed} [thisArg] The `this` binding for the callback.
   * @returns {Boolean} Returns `true` if any value passes the callback check, else `false`.
   * @example
   *
   * _.some([null, 0, 'yes', false]);
   * // => true
   */
  var some = iterationFactory(forEachFactoryOptions, everyFactoryOptions, {
    'init': 'false',
    'inLoop': everyFactoryOptions.inLoop.replace('!', '')
  });

  /**
   * Uses a binary search to determine the index at which the `value` should be
   * inserted into the `collection` in order to maintain the `collection`'s sorted
   * order. If `callback` is passed, it will be executed for each value in the
   * `collection` to compute their sort ranking. The `callback` is invoked with
   * 1 arguments.
   *
   * @static
   * @memberOf _
   * @category Collections
   * @param {Array} array The array to iterate over.
   * @param {Mixed} value The value to evaluate.
   * @param {Function} [callback] The function called per iteration.
   * @returns {Number} Returns the index at which the value should be inserted
   *  into the collection.
   * @example
   *
   * _.sortedIndex([10, 20, 30, 40, 50], 35);
   * // => 3
   */
  function sortedIndex(array, object, callback) {
    var low = 0,
        high = array.length;

    callback || (callback = identity);
    while (low < high) {
      var mid = (low + high) >> 1;
      callback(array[mid]) < callback(object) ? (low = mid + 1) : (high = mid);
    }
    return low;
  }

  /**
   * Converts the `collection`, into an array. Useful for converting the
   * `arguments` object.
   *
   * @static
   * @memberOf _
   * @category Collections
   * @param {Array|Object} collection The collection to convert.
   * @returns {Array} Returns the new converted array.
   * @example
   *
   * (function() { return _.toArray(arguments).slice(1); })(1, 2, 3, 4);
   * // => [2, 3, 4]
   */
  function toArray(collection) {
    if (!collection) {
      return [];
    }
    if (isArray(collection) || isArguments(collection)) {
      return slice.call(collection);
    }
    if (isFunction(collection.toArray)) {
      return collection.toArray();
    }
    return values(collection);
  }

  /**
   * Produces an array of enumerable own property values of the `collection`.
   *
   * @static
   * @memberOf _
   * @alias methods
   * @category Collections
   * @param {Array|Object} collection The collection to inspect.
   * @returns {Array} Returns a new array of property values.
   * @example
   *
   * _.values({ 'one': 1, 'two': 2, 'three': 3 });
   * // => [1, 2, 3]
   */
  var values = iterationFactory(mapFactoryOptions, {
    'args': 'collection',
    'inLoop': {
      'array': 'result[index]=collection[index]',
      'object': 'result[result.length]=collection[index]'
    }
  });

  /*--------------------------------------------------------------------------*/

  /**
   * Produces a new array with all falsey values of `array` removed. The values
   * `false`, `null`, `0`, `""`, `undefined` and `NaN` are all falsey.
   *
   * @static
   * @memberOf _
   * @category Arrays
   * @param {Array} array The array to compact.
   * @returns {Array} Returns a new filtered array.
   * @example
   *
   * _.compact([0, 1, false, 2, '', 3]);
   * // => [1, 2, 3]
   */
  var compact = iterationFactory({
    'args': 'array',
    'init': '[]',
    'inLoop': 'if(array[index])result.push(array[index])'
  });

  /**
   * Produces a new array of `array` values not present in the other arrays
   * using strict equality for comparisons, i.e. `===`.
   *
   * @static
   * @memberOf _
   * @category Arrays
   * @param {Array} array The array to process.
   * @param {Mixed} [array1, array2, ...] Arrays to check.
   * @returns {Array} Returns a new array of `array` values not present in the
   *  other arrays.
   * @example
   *
   * _.difference([1, 2, 3, 4, 5], [5, 2, 10]);
   * // => [1, 3, 4]
   */
  var difference = iterationFactory(differenceFactoryOptions);

  /**
   * Gets the first value of the `array`. Pass `n` to return the first `n` values
   * of the `array`.
   *
   * @static
   * @memberOf _
   * @alias head, take
   * @category Arrays
   * @param {Array} array The array to query.
   * @param {Number} [n] The number of elements to return.
   * @param {Object} [guard] Internally used to allow this method to work with
   *  others like `_.map` without using their callback `index` argument for `n`.
   * @returns {Mixed} Returns the first value or an array of the first `n` values
   *  of the `array`.
   * @example
   *
   * _.first([5, 4, 3, 2, 1]);
   * // => 5
   */
  function first(array, n, guard) {
    return (n == undefined || guard) ? array[0] : slice.call(array, 0, n);
  }

  /**
   * Flattens a nested array (the nesting can be to any depth). If `shallow` is
   * truthy, `array` will only be flattened a single level.
   *
   * @static
   * @memberOf _
   * @category Arrays
   * @param {Array} array The array to compact.
   * @param {Boolean} shallow A flag to indicate only flattening a single level.
   * @returns {Array} Returns a new flattened array.
   * @example
   *
   * _.flatten([1, [2], [3, [[4]]]]);
   * // => [1, 2, 3, 4];
   *
   * _.flatten([1, [2], [3, [[4]]]], true);
   * // => [1, 2, 3, [[4]]];
   */
  function flatten(array, shallow) {
    if (shallow) {
      return concat.apply([], array);
    }
    return reduce(array, function(accumulator, value) {
      if (isArray(value)) {
        push.apply(accumulator, flatten(value));
        return accumulator;
      }
      accumulator.push(value);
      return accumulator;
    }, []);
  }

  /**
   * Gets the index at which the first occurrence of `value` is found using
   * strict equality for comparisons, i.e. `===`. If the `array` is already
   * sorted, passing `true` for `isSorted` will run a faster binary search.
   *
   * @static
   * @memberOf _
   * @category Arrays
   * @param {Array} array The array to search.
   * @param {Mixed} value The value to search for.
   * @param {Boolean} [isSorted=false] A flag to indicate that the `array` is already sorted.
   * @returns {Number} Returns the index of the matched value or `-1`.
   * @example
   *
   * _.indexOf([1, 2, 3], 2);
   * // => 1
   */
  function indexOf(array, value, isSorted) {
    var index, length;
    if (array == undefined) {
      return -1;
    }
    if (isSorted) {
      index = sortedIndex(array, value);
      return array[index] === value ? index : -1;
    }
    for (index = 0, length = array.length; index < length; index++) {
      if (array[index] === value) {
        return index;
      }
    }
    return -1;
  }

  /**
   * Gets all but the last value of the `array`. Pass `n` to exclude the last `n`
   * values from the result.
   *
   * @static
   * @memberOf _
   * @category Arrays
   * @param {Array} array The array to query.
   * @param {Number} [n] The number of elements to return.
   * @param {Object} [guard] Internally used to allow this method to work with
   *  others like `_.map` without using their callback `index` argument for `n`.
   * @returns {Array} Returns all but the last value or `n` values of the `array`.
   * @example
   *
   * _.initial([5, 4, 3, 2, 1]);
   * // => [5, 4, 3, 2]
   */
  function initial(array, n, guard) {
    return slice.call(array, 0, -((n == undefined || guard) ? 1 : n));
  }

  /**
   * Computes the intersection of all the passed-in arrays.
   *
   * @static
   * @memberOf _
   * @alias intersect
   * @category Arrays
   * @param {Mixed} [array1, array2, ...] Arrays to process.
   * @returns {Array} Returns a new array of unique values, in order, that are
   *  present in **all** of the arrays.
   * @example
   *
   * _.intersection([1, 2, 3], [101, 2, 1, 10], [2, 1]);
   * // => [1, 2]
   */
  function intersection(array) {
    var rest = slice.call(arguments, 1);
    return filter(uniq(array), function(value) {
      return every(rest, function(other) {
        return indexOf(other, value) >= 0;
      });
    });
  }

  /**
   * Gets the last value of the `array`. Pass `n` to return the lasy `n` values
   * of the `array`.
   *
   * @static
   * @memberOf _
   * @category Arrays
   * @param {Array} array The array to query.
   * @param {Number} [n] The number of elements to return.
   * @param {Object} [guard] Internally used to allow this method to work with
   *  others like `_.map` without using their callback `index` argument for `n`.
   * @returns {Array} Returns all but the last value or `n` values of the `array`.
   * @example
   *
   * _.last([5, 4, 3, 2, 1]);
   * // => 1
   */
  function last(array, n, guard) {
    var length = array.length;
    return (n == undefined || guard) ? array[length - 1] : slice.call(array, -n || length);
  }

  /**
   * Gets the index at which the last occurrence of `value` is found using
   * strict equality for comparisons, i.e. `===`.
   *
   * @static
   * @memberOf _
   * @category Arrays
   * @param {Array} array The array to search.
   * @param {Mixed} value The value to search for.
   * @returns {Number} Returns the index of the matched value or `-1`.
   * @example
   *
   * _.lastIndexOf([1, 2, 3, 1, 2, 3], 2);
   * // => 4
   */
  function lastIndexOf(array, value) {
    if (array == undefined) {
      return -1;
    }
    var index = array.length;
    while (index--) {
      if (array[index] === value) {
        return index;
      }
    }
    return -1;
  }

  /**
   * Creates an array of numbers (positive and/or negative) progressing from
   * `start` up to but not including `stop`. This method is a port of Python's
   * `range()` function. See http://docs.python.org/library/functions.html#range.
   *
   * @static
   * @memberOf _
   * @category Arrays
   * @param {Number} [start=0] The start of the range.
   * @param {Number} end The end of the range.
   * @param {Number} [step=1] The value to increment or descrement by.
   * @returns {Array} Returns a new range array.
   * @example
   *
   * _.range(10);
   * // => [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
   *
   * _.range(1, 11);
   * // => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
   *
   * _.range(0, 30, 5);
   * // => [0, 5, 10, 15, 20, 25]
   *
   * _.range(0, -10, -1);
   * // => [0, -1, -2, -3, -4, -5, -6, -7, -8, -9]
   *
   * _.range(0);
   * // => []
   */
  function range(start, end, step) {
    step || (step = 1);
    if (arguments.length < 2) {
      end = start || 0;
      start = 0;
    }

    var index = -1,
        length = Math.max(Math.ceil((end - start) / step), 0),
        result = Array(length);

    while (++index < length) {
      result[index] = start;
      start += step;
    }
    return result;
  }

  /**
   * The opposite of `_.initial`, this method gets all but the first value of
   * the `array`. Pass `n` to exclude the first `n` values from the result.
   *
   * @static
   * @memberOf _
   * @alias tail
   * @category Arrays
   * @param {Array} array The array to query.
   * @param {Number} [n] The number of elements to return.
   * @param {Object} [guard] Internally used to allow this method to work with
   *  others like `_.map` without using their callback `index` argument for `n`.
   * @returns {Array} Returns all but the first value or `n` values of the `array`.
   * @example
   *
   * _.rest([5, 4, 3, 2, 1]);
   * // => [4, 3, 2, 1]
   */
  function rest(array, n, guard) {
    return slice.call(array, (n == undefined || guard) ? 1 : n);
  }

  /**
   * Computes the union of the passed-in arrays.
   *
   * @static
   * @memberOf _
   * @category Arrays
   * @param {Mixed} [array1, array2, ...] Arrays to process.
   * @returns {Array} Returns a new array of unique values, in order, that are
   *  present in one or more of the arrays.
   * @example
   *
   * _.union([1, 2, 3], [101, 2, 1, 10], [2, 1]);
   * // => [1, 2, 3, 101, 10]
   */
  function union() {
    return uniq(flatten(arguments, true));
  }

  /**
   * Produces a duplicate-value-free version of the `array` using strict equality
   * for comparisons, i.e. `===`. If the `array` is already sorted, passing `true`
   * for `isSorted` will run a faster algorithm. If `callback` is passed,
   * each value of `array` is passed through a transformation `callback` before
   * uniqueness is computed. The `callback` is invoked with 3 arguments;
   * (value, index, array).
   *
   * @static
   * @memberOf _
   * @alias unique
   * @category Arrays
   * @param {Array} array The array to process.
   * @param {Boolean} [isSorted=false] A flag to indicate that the `array` is already sorted.
   * @param {Function} [callback] A
   * @returns {Array} Returns a duplicate-value-free array.
   * @example
   *
   * _.uniq([1, 2, 1, 3, 1, 4]);
   * // => [1, 2, 3, 4]
   */
  function uniq(array, isSorted, callback) {
    var initial = callback ? map(array, callback) : array,
        result = [];

    // the `isSorted` flag is irrelevant if the array only contains two elements.
    if (array.length < 3) {
      isSorted = true;
    }
    reduce(initial, function(accumulator, value, index) {
      if (isSorted ? last(accumulator) !== value || !accumulator.length : indexOf(accumulator, value) < 0) {
        accumulator.push(value);
        result.push(array[index]);
      }
      return accumulator;
    }, []);

    return result;
  }

  /**
   * Produces a new array with all occurrences of the values removed using strict
   * equality for comparisons, i.e. `===`.
   *
   * @static
   * @memberOf _
   * @category Arrays
   * @param {Array} array The array to filter.
   * @param {Mixed} [value1, value2, ...] Values to remove.
   * @returns {Array} Returns a new filtered array.
   * @example
   *
   * _.without([1, 2, 1, 0, 3, 1, 4], 0, 1);
   * // => [2, 3, 4]
   */
  var without = iterationFactory(differenceFactoryOptions, {
    'top': 'var values=slice.call(arguments,1)',
    'init': '[]'
  });

  /**
   * Merges together the values of each of the arrays with the value at the
   * corresponding position. Useful for separate data sources that are coordinated
   * through matching array indexes. For a matrix of nested arrays, `_.zip.apply(...)`
   * can transpose the matrix in a similar fashion.
   *
   * @static
   * @memberOf _
   * @category Arrays
   * @param {Mixed} [array1, array2, ...] Arrays to process.
   * @returns {Array} Returns a new array of merged arrays.
   * @example
   *
   * _.zip(['moe', 'larry', 'curly'], [30, 40, 50], [true, false, false]);
   * // => [['moe', 30, true], ['larry', 40, false], ['curly', 50, false]]
   */
  function zip() {
    var index = -1,
        length = max(pluck(arguments, 'length')),
        result = Array(length);

    while (++index < length) {
      result[index] = pluck(arguments, index);
    }
    return result;
  }

  /*--------------------------------------------------------------------------*/

  /**
   * Creates a new function that is restricted to executing only after it is
   * called a given number of `times`.
   *
   * @static
   * @memberOf _
   * @category Functions
   * @param {Number} times The number of times the function must be called before
   * it is executed.
   * @param {Function} func The function to restrict.
   * @returns {Function} Returns the new restricted function.
   * @example
   *
   * var renderNotes = _.after(notes.length, render);
   * _.forEach(notes, function(note) {
   *   note.asyncSave({ 'success': renderNotes });
   * });
   * // renderNotes is run once, after all notes have saved.
   */
  function after(times, func) {
    if (times < 1) {
      return func();
    }
    return function() {
      if (--times < 1) {
        return func.apply(this, arguments);
      }
    };
  }

  /**
   * Creates a new function that, when called, invokes `func` with the `this`
   * binding of `thisArg` and prepends additional arguments to those passed to
   * the bound function.
   *
   * @static
   * @memberOf _
   * @category Functions
   * @param {Function} func The function to bind.
   * @param @param {Mixed} [thisArg] The `this` binding of `func`.
   * @param {Mixed} [arg1, arg2, ...] Arguments to prepend to those passed to the bound function.
   * @returns {Function} Returns the new bound function.
   * @example
   *
   * var func = function(greeting) { return greeting + ': ' + this.name; };
   * func = _.bind(func, { 'name': 'moe' }, 'hi');
   * func();
   * // => 'hi: moe'
   */
  function bind(func, thisArg) {
    var args = slice.call(arguments, 2),
        argsLength = args.length;

    return function() {
      args.length = argsLength;
      push.apply(args, arguments);
      return func.apply(thisArg, args);
    };
  }

  /**
   * Binds methods on the `object` to the object, overwriting the non-bound method.
   * If no method names are provided, all the function properties of the `object`
   * will be bound.
   *
   * @static
   * @memberOf _
   * @category Functions
   * @param {Object} object The object to bind and assign the bound methods to.
   * @param {Mixed} [methodName1, methodName2, ...] Method names on the object to bind.
   * @returns {Object} Returns the `object`.
   * @example
   *
   * var buttonView = {
   *  'label': 'lodash',
   *  'onClick': function() { alert('clicked: ' + this.label); },
   *  'onHover': function() { console.log('hovering: ' + this.label); }
   * };
   *
   * _.bindAll(buttonView);
   * jQuery('#lodash_button').on('click', buttonView.onClick);
   * // => When the button is clicked, `this.label` will have the correct value
   */
  function bindAll(object) {
    var funcs = arguments,
        index = 1;

    if (funcs.length == 1) {
      index = 0;
      funcs = functions(object);
    }
    for (var length = funcs.length; index < length; index++) {
      object[funcs[index]] = bind(object[funcs[index]], object);
    }
    return object;
  }

  /**
   * Creates a new function that is the composition of the passed functions,
   * where each function consumes the return value of the function that follows.
   * In math terms, composing thefunctions `f()`, `g()`, and `h()` produces `f(g(h()))`.
   *
   * @static
   * @memberOf _
   * @category Functions
   * @param {Mixed} [func1, func2, ...] Functions to compose.
   * @returns {Function} Returns the new composed function.
   * @example
   *
   * var greet = function(name) { return 'hi: ' + name; };
   * var exclaim = function(statement) { return statement + '!'; };
   * var welcome = _.compose(exclaim, greet);
   * welcome('moe');
   * // => 'hi: moe!'
   */
  function compose() {
    var funcs = arguments;
    return function() {
      var args = arguments,
          length = funcs.length;

      while (length--) {
        args = [funcs[length].apply(this, args)];
      }
      return args[0];
    };
  }

  /**
   * Creates a new function that will postpone its execution until after `wait`
   * milliseconds have elapsed since the last time it was invoked. Pass `true`
   * for `immediate` to cause debounce to invoke the function on the leading,
   * instead of the trailing, edge of the `wait` timeout.
   *
   * @static
   * @memberOf _
   * @category Functions
   * @param {Function} func The function to debounce.
   * @param {Number} wait The number of milliseconds to postone.
   * @param {Boolean} immediate A flag to indicate execution is on the leading
   *  edge of the timeout.
   * @returns {Function} Returns the new debounced function.
   * @example
   *
   * var lazyLayout = _.debounce(calculateLayout, 300);
   * jQuery(window).on('resize', lazyLayout);
   */
  function debounce(func, wait, immediate) {
    var timeout;
    return function() {
      var args = arguments,
          thisArg = this;

      if (immediate && !timeout) {
        func.apply(thisArg, args);
      }
      clearTimeout(timeout);
      timeout = setTimeout(function() {
        timeout = undefined;
        if (!immediate) {
          func.apply(thisArg, args);
        }
      }, wait);
    };
  }

  /**
   * Invokes the `func` function after `wait` milliseconds. Additional arguments
   * are passed `func` when it is invoked.
   *
   * @static
   * @memberOf _
   * @category Functions
   * @param {Function} func The function to delay.
   * @param {Number} wait The number of milliseconds to delay execution.
   * @param {Mixed} [arg1, arg2, ...] Arguments to invoke the function with.
   * @returns {Number} Returns the `setTimeout` timeout id.
   * @example
   *
   * var log = _.bind(console.log, console);
   * _.delay(log, 1000, 'logged later');
   * // => 'logged later' (Appears after one second.)
   */
  function delay(func, wait) {
    var args = slice.call(arguments, 2);
    return setTimeout(function() { return func.apply(undefined, args); }, wait);
  }

  /**
   * Defers invoking the `func` function until the current call stack has cleared.
   * Additional arguments are passed to `func` when it is invoked.
   *
   * @static
   * @memberOf _
   * @category Functions
   * @param {Function} func The function to defer.
   * @param {Mixed} [arg1, arg2, ...] Arguments to invoke the function with.
   * @returns {Number} Returns the `setTimeout` timeout id.
   * @example
   *
   * _.defer(function() { alert('deferred'); });
   * // Returns from the function before the alert runs.
   */
  function defer(func) {
    var args = slice.call(arguments, 1);
    return setTimeout(function() { return func.apply(undefined, args); }, 1);
  }

  /**
   * Creates a new function that memoizes the result of `func`. If `resolver` is
   * passed, it will be used to determine the cache key for storing the result
   * based on the arguments passed to the memoized function. By default, the first
   * argument passed to the memoized function is used as the cache key.
   *
   * @static
   * @memberOf _
   * @category Functions
   * @param {Function} func The function to have its output memoized.
   * @param {Function} [resolver] A function used to resolve the cache key.
   * @returns {Function} Returns the new memoizing function.
   * @example
   *
   * var fibonacci = _.memoize(function(n) {
   *   return n < 2 ? n : fibonacci(n - 1) + fibonacci(n - 2);
   * });
   */
  function memoize(func, resolver) {
    var cache = {};
    return function() {
      var prop = resolver ? resolver.apply(this, arguments) : arguments[0];
      return hasOwnProperty.call(cache, prop)
        ? cache[prop]
        : (cache[prop] = func.apply(this, arguments));
    };
  }

  /**
   * Creates a new function that is restricted to one execution. Repeat calls to
   * the function will return the value of the first call.
   *
   * @static
   * @memberOf _
   * @category Functions
   * @param {Function} func The function to restrict.
   * @returns {Function} Returns the new restricted function.
   * @example
   *
   * var initialize = _.once(createApplication);
   * initialize();
   * initialize();
   * // Application is only created once.
   */
  function once(func) {
    var result,
        ran = false;

    return function() {
      if (ran) {
        return result;
      }
      ran = true;
      result = func.apply(this, arguments);
      return result;
    };
  }

  /**
   * Creates a new function that, when invoked, will only call the original
   * function at most once per every `wait` milliseconds.
   *
   * @static
   * @memberOf _
   * @category Functions
   * @param {Function} func The function to throttle.
   * @param {Number} wait The number of milliseconds to throttle executions to.
   * @returns {Function} Returns the new throttled function.
   * @example
   *
   * var throttled = _.throttle(updatePosition, 100);
   * jQuery(window).on('scroll', throttled);
   */
  function throttle(func, wait) {
    var args, more, result, thisArg, throttling, timeout,
        whenDone = debounce(function() { more = throttling = false; }, wait);

    return function() {
      args = arguments;
      thisArg = this;

      if (!timeout) {
        timeout = setTimeout(function() {
          timeout = undefined;
          if (more) {
            func.apply(thisArg, args);
          }
          whenDone();
        }, wait);
      }
      if (throttling) {
        more = true;
      } else {
        result = func.apply(thisArg, args);
      }
      whenDone();
      throttling = true;
      return result;
    };
  }

  /**
   * Create a new function that passes the `func` function to the `wrapper`
   * function as its first argument. Additional arguments are appended to those
   * passed to the `wrapper` function.
   *
   * @static
   * @memberOf _
   * @category Functions
   * @param {Function} func The function to wrap.
   * @param {Function} wrapper The wrapper function.
   * @param {Mixed} [arg1, arg2, ...] Arguments to append to those passed to the wrapper.
   * @returns {Function} Returns the new function.
   * @example
   *
   * var hello = function(name) { return 'hello: ' + name; };
   * hello = _.wrap(hello, function(func) {
   *   return 'before, ' + func('moe') + ', after';
   * });
   * hello();
   * // => 'before, hello: moe, after'
   */
  function wrap(func, wrapper) {
    return function() {
      var args = [func];
      push.apply(args, arguments);
      return wrapper.apply(this, args);
    };
  }

  /*--------------------------------------------------------------------------*/

  /**
   * Create a shallow clone of the `value`. Any nested objects or arrays will be
   * assigned by reference and not cloned.
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Mixed} value The value to clone.
   * @returns {Mixed} Returns the cloned `value`.
   * @example
   *
   * _.clone({ 'name': 'moe' });
   * // => { 'name': 'moe' };
   */
  function clone(value) {
    if (value !== Object(value)) {
      return value;
    }
    return isArray(value) ? value.slice() : extend({}, value);
  }

  /**
   * Assigns missing properties in `object` with default values from the defaults
   * objects. As soon as a property is set, additional defaults of the same
   * property will be ignored.
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Object} object The object to populate.
   * @param {Object} [defaults1, defaults2, ..] The defaults objects to apply to `object`.
   * @returns {Object} Returns `object`.
   * @example
   *
   * var iceCream = { 'flavor': 'chocolate' };
   * _.defaults(iceCream, { 'flavor': 'vanilla', 'sprinkles': 'lots' });
   * // => { 'flavor': 'chocolate', 'sprinkles': 'lots' }
   */
  var defaults = iterationFactory(extendFactoryOptions, {
    'inLoop': 'if(object[index]==undefined)' + extendFactoryOptions.inLoop
  });

  /**
   * Copies enumerable properties from the source objects to the `destination` object.
   * Subsequent sources will overwrite propery assignments of previous sources.
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Object} object The destination object.
   * @param {Object} [source1, source2, ..] The source objects.
   * @returns {Object} Returns the destination object.
   * @example
   *
   * _.extend({ 'name': 'moe' }, { 'age': 40 });
   * // => { 'name': 'moe', 'age': 40 }
   */
  var extend = iterationFactory(extendFactoryOptions);

  /**
   * Produces a sorted array of the properties, own and inherited, of `object`
   * that have function values.
   *
   * @static
   * @memberOf _
   * @alias methods
   * @category Objects
   * @param {Object} object The object to inspect.
   * @returns {Array} Returns a new array of property names that have function values.
   * @example
   *
   * _.functions(_);
   * // => ['all', 'any', 'bind', 'bindAll', 'clone', 'compact', 'compose', ...]
   */
  var functions = iterationFactory(keysFactoryOptions, {
    'top': '',
    'useHas': false,
    'inLoop': 'if(toString.call(object[index])==funcClass)result.push(index)',
    'returns': 'result.sort()'
  });

  /**
   * Checks if the specified object `property` exists and is a direct property,
   * instead of an inherited property.
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Object} object The object to check.
   * @param {String} property The property to check for.
   * @returns {Boolean} Returns `true` if key is a direct property, else `false`.
   * @example
   *
   * _.has({ 'a': 1, 'b': 2, 'c': 3 }, 'b');
   * // => true
   */
  function has(object, prop) {
    return hasOwnProperty.call(object, prop);
  }

  /**
   * Checks if a `value` is an `arguments` object.
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Mixed} value The value to check.
   * @returns {Boolean} Returns `true` if the `value` is an `arguments` object, else `false`.
   * @example
   *
   * (function() { return _.isArguments(arguments); })(1, 2, 3);
   * // => true
   *
   * _.isArguments([1, 2, 3]);
   * // => false
   */
  var isArguments = function isArguments(value) {
    return toString.call(value) == '[object Arguments]';
  };
  // fallback for browser like IE<9 which detect `arguments` as `[object Object]`
  if (!isArguments(arguments)) {
    isArguments = function isArguments(value) {
      return !!(value && hasOwnProperty.call(value, 'callee'));
    };
  }

  /**
   * Checks if a `value` is a boolean (`true` or `false`) value.
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Mixed} value The value to check.
   * @returns {Boolean} Returns `true` if the `value` is a boolean value, else `false`.
   * @example
   *
   * _.isBoolean(null);
   * // => false
   */
  function isBoolean(value) {
    return value === true || value === false || toString.call(value) == boolClass;
  }

  /**
   * Checks if a `value` is a date.
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Mixed} value The value to check.
   * @returns {Boolean} Returns `true` if the `value` is a date, else `false`.
   * @example
   *
   * _.isDate(new Date);
   * // => true
   */
  function isDate(value) {
    return toString.call(value) == dateClass;
  }

  /**
   * Checks if a `value` is a DOM element.
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Mixed} value The value to check.
   * @returns {Boolean} Returns `true` if the `value` is a DOM element, else `false`.
   * @example
   *
   * _.isElement(document.body);
   * // => true
   */
  function isElement(value) {
    return !!(value && value.nodeType == 1);
  }

  /**
   * Performs a deep comparison between two values to determine if they are
   * equivalent to each other.
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Mixed} a The value to compare.
   * @param {Mixed} b The other value to compare.
   * @param {Array} [stack] Internally used to keep track of "seen" objects to
   *  avoid circular references.
   * @returns {Boolean} Returns `true` if the values are equvalent, else `false`.
   * @example
   *
   * var moe = { 'name': 'moe', 'luckyNumbers': [13, 27, 34] };
   * var clone = { 'name': 'moe', 'luckyNumbers': [13, 27, 34] };
   *
   * moe == clone;
   * // => false
   *
   * _.isEqual(moe, clone);
   * // => true
   */
  function isEqual(a, b, stack) {
    stack || (stack = []);

    // exit early for identical values
    if (a === b) {
      // treat `+0` vs. `-0` as not equal
      return a !== 0 || (1 / a == 1 / b);
    }
    // a strict comparison is necessary because `null == undefined`
    if (a == undefined || b == undefined) {
      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 stringClass:
        // primitives and their corresponding object instances are equivalent;
        // thus, `'5'` is quivalent to `new String('5')`
        return a == String(b);

      case numberClass:
        // treat `NaN` vs. `NaN` as equal
        return a != +a
          ? b != +b
          // but treat `+0` vs. `-0` as not equal
          : (a == 0 ? (1 / a == 1 / b) : a == +b);

      case boolClass:
      case dateClass:
        // coerce dates and booleans to numeric values, dates to milliseconds and booleans to 1 or 0;
        // treat invalid dates coerced to `NaN` as not equal
        return +a == +b;

      // regexps are compared by their source and flags
      case regexpClass:
        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;
      }
    }

    var result = true,
        size = 0;

    // add the first collection to the stack of traversed objects
    stack.push(a);

    // recursively compare objects and arrays
    if (className == arrayClass) {
      // 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 && isEqual(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 prop in a) {
        if (hasOwnProperty.call(a, prop)) {
          // count the expected number of properties
          size++;
          // deep compare each member
          if (!(result = hasOwnProperty.call(b, prop) && isEqual(a[prop], b[prop], stack))) {
            break;
          }
        }
      }
      // ensure that both objects contain the same number of properties
      if (result) {
        for (prop in b) {
          if (hasOwnProperty.call(b, prop) && !(size--)) {
            break;
          }
        }
        result = !size;
      }
    }
    // remove the first collection from the stack of traversed objects
    stack.pop();
    return result;
  }

  /**
   * Checks if a `value` is a finite number.
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Mixed} value The value to check.
   * @returns {Boolean} Returns `true` if the `value` is a finite number, else `false`.
   * @example
   *
   * _.isFinite(-101);
   * // => true
   *
   * _.isFinite('10');
   * // => false
   *
   * _.isFinite(Infinity);
   * // => false
   */
  function isFinite(value) {
    return nativeIsFinite(value) && toString.call(value) == numberClass;
  }

  /**
   * Checks if a `value` is a function.
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Mixed} value The value to check.
   * @returns {Boolean} Returns `true` if the `value` is a function, else `false`.
   * @example
   *
   * _.isFunction(''.concat);
   * // => true
   */
  function isFunction(value) {
    return toString.call(value) == funcClass;
  }

  /**
   * Checks if a `value` is an object.
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Mixed} value The value to check.
   * @returns {Boolean} Returns `true` if the `value` is an object, else `false`.
   * @example
   *
   * _.isObject({});
   * // => true
   *
   * _.isObject(1);
   * // => false
   */
  function isObject(value) {
    return value === Object(value);
  }

  /**
   * Checks if a `value` is `NaN`.
   * Note: this is not the same as native `isNaN`, which will return true for
   * `undefined` and other values. See http://es5.github.com/#x15.1.2.4.
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Mixed} value The value to check.
   * @returns {Boolean} Returns `true` if the `value` is `NaN`, else `false`.
   * @example
   *
   * _.isNaN(NaN);
   * // => true
   *
   * _.isNaN(new Number(NaN));
   * // => true
   *
   * isNaN(undefined);
   * // => true
   *
   * _.isNaN(undefined);
   * // => false
   */
  function isNaN(value) {
    // `NaN` as a primitive is the only value that is not equal to itself
    return value != +value && toString.call(value) == numberClass;
  }

  /**
   * Checks if a `value` is `null`.
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Mixed} value The value to check.
   * @returns {Boolean} Returns `true` if the `value` is `null`, else `false`.
   * @example
   *
   * _.isNull(null);
   * // => true
   *
   * _.isNull(undefined);
   * // => false
   */
  function isNull(value) {
    return value === null;
  }

  /**
   * Checks if a `value` is a number.
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Mixed} value The value to check.
   * @returns {Boolean} Returns `true` if the `value` is a number, else `false`.
   * @example
   *
   * _.isNumber(8.4 * 5;
   * // => true
   */
  function isNumber(value) {
    return toString.call(value) == numberClass;
  }

  /**
   * Checks if a `value` is a regular expression.
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Mixed} value The value to check.
   * @returns {Boolean} Returns `true` if the `value` is a regular expression, else `false`.
   * @example
   *
   * _.isRegExp(/moe/);
   * // => true
   */
  function isRegExp(value) {
    return toString.call(value) == regexpClass;
  }

  /**
   * Checks if a `value` is a string.
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Mixed} value The value to check.
   * @returns {Boolean} Returns `true` if the `value` is a string, else `false`.
   * @example
   *
   * _.isString('moe');
   * // => true
   */
  function isString(value) {
    return toString.call(value) == stringClass;
  }

  /**
   * Checks if a `value` is `undefined`.
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Mixed} value The value to check.
   * @returns {Boolean} Returns `true` if the `value` is `undefined`, else `false`.
   * @example
   *
   * _.isUndefined(void 0);
   * // => true
   */
  function isUndefined(value) {
    return value === undefined;
  }

  /**
   * Produces an array of the `object`'s enumerable own property names.
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Object} object The object to inspect.
   * @returns {Array} Returns a new array of property names.
   * @example
   *
   * _.keys({ 'one': 1, 'two': 2, 'three': 3 });
   * // => ['one', 'two', 'three']
   */
  var keys = nativeKeys || iterationFactory(keysFactoryOptions);

  /**
   * Creates an object composed of the specified properties. Property names may
   * be specified as individual arguments or as arrays of property names.
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Object} object The object to pluck.
   * @param {Object} [prop1, prop2, ..] The properties to pick.
   * @returns {Object} Returns an object composed of the picked properties.
   * @example
   *
   * _.pick({ 'name': 'moe', 'age': 40, 'userid': 'moe1' }, 'name', 'age');
   * // => { 'name': 'moe', 'age': 40 }
   */
  function pick(object) {
    var prop,
        index = -1,
        props = flatten(slice.call(arguments, 1)),
        length = props.length,
        result = {};

    while (++index < length) {
      prop = props[index];
      if (prop in object) {
        result[prop] = object[prop];
      }
    }
    return result;
  }

  /**
   * Invokes `interceptor` with the `value` as the first argument, and then returns
   * `value`. The primary purpose of this method is to "tap into" a method chain,
   * in order to performoperations on intermediate results within the chain.
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Mixed} value The value to pass to `callback`.
   * @param {Function} interceptor The function to invoke.
   * @returns {Mixed} Returns `value`.
   * @example
   *
   * _.chain([1,2,3,200])
   *  .filter(function(num) { return num % 2 == 0; })
   *  .tap(alert)
   *  .map(function(num) { return num * num })
   *  .value();
   * // => // [2, 200] (alerted)
   * // => [4, 40000]
   */
  function tap(value, interceptor) {
    interceptor(value);
    return value;
  }

  /*--------------------------------------------------------------------------*/

  /**
   * Escapes a string for insertion into HTML, replacing `&`, `<`, `>`, `"`, `'`,
   * and `/` characters.
   *
   * @static
   * @memberOf _
   * @category Utilities
   * @param {String} string The string to escape.
   * @returns {String} Returns the escaped string.
   * @example
   *
   * _.escape('Curly, Larry & Moe');
   * // => "Curly, Larry &amp; Moe"
   */
  function escape(string) {
    return (string + '')
      .replace(/&/g, '&amp;')
      .replace(/</g, '&lt;')
      .replace(/>/g, '&gt;')
      .replace(/"/g, '&quot;')
      .replace(/'/g, '&#x27;')
      .replace(/\//g,'&#x2F;');
  }

  /**
   * This function simply returns the first argument passed to it.
   * Note: It is used throughout Lo-Dash as a default callback.
   *
   * @static
   * @memberOf _
   * @category Utilities
   * @param {Mixed} value Any value.
   * @returns {Mixed} Returns `value`.
   * @example
   *
   * var moe = { 'name': 'moe' };
   * moe === _.identity(moe);
   * // => true
   */
  function identity(value) {
    return value;
  }

  /**
   * Adds functions properties of `object` to the `lodash` function and chainable
   * wrapper.
   *
   * @static
   * @memberOf _
   * @category Utilities
   * @param {Object} object The object of function properties to add to `lodash`.
   * @example
   *
   * _.mixin({
   *   'capitalize': function(string) {
   *     return string.charAt(0).toUpperCase() + string.slice(1).toLowerCase();
   *   }
   * });
   *
   * _.capitalize('curly');
   * // => 'Curly'
   *
   * _('larry').capitalize();
   * // => 'Larry'
   */
  function mixin(object) {
    forEach(functions(object), function(methodName) {
      var func = lodash[methodName] = object[methodName];

      lodash.prototype[methodName] = function() {
        // In Opera < 9.50 and some older/beta Mobile Safari versions using `unshift()`
        // generically to augment the `arguments` object will pave the value at
        // index `0` without incrimenting the other values's indexes.
        // https://github.com/documentcloud/underscore/issues/9
        var args = slice.call(arguments);
        unshift.call(args, this._wrapped);

        var result = func.apply(lodash, args);
        return this._chain ? new Lodash(result).chain() : result;
      };
    });
  }

  /**
   * Reverts the '_' variable to its previous value and returns a reference to
   * the `lodash` function.
   *
   * @static
   * @memberOf _
   * @category Utilities
   * @returns {Function} Returns the `lodash` function.
   * @example
   *
   * var lodash = _.noConflict();
   */
  function noConflict() {
    window._ = oldDash;
    return this;
  }

  /**
   * Resolves the value of `property` on `object`. If the property is a function
   * it will be invoked and its result returned, else the property value is returned.
   *
   * @static
   * @memberOf _
   * @category Utilities
   * @param {Object} object The object to inspect.
   * @param {String} property The property to get the result of.
   * @returns {Mixed} Returns the resolved.
   * @example
   *
   * var object = {
   *   'cheese': 'crumpets',
   *   'stuff': function() {
   *     return 'nonsense';
   *   }
   * };
   *
   * _.result(object, 'cheese');
   * // => 'crumpets'
   *
   * _.result(object, 'stuff');
   * // => 'nonsense'
   */
  function result(object, property) {
    if (object == undefined) {
      return null;
    }
    var value = object[property];
    return isFunction(value) ? object[property]() : value;
  }

  /**
   * Executes the `callback` function `n` times.
   *
   * @static
   * @memberOf _
   * @category Utilities
   * @param {Number} n The number of times to execute the callback.
   * @param {Function} callback The function called per iteration.
   * @param {Mixed} [thisArg] The `this` binding for the callback.
   * @example
   *
   * _.times(3, function() { genie.grantWish(); });
   */
  function times(n, callback, thisArg) {
    if (thisArg) {
      callback = bind(callback, thisArg);
    }
    for (var index = 0; index < n; index++) {
      callback(index);
    }
  }

  /**
   * Generates a unique id. If `prefix` is passed, the id will be appended to it.
   *
   * @static
   * @memberOf _
   * @category Utilities
   * @param {String} [prefix] The value to prefix the id with.
   * @returns {Number|String} Returns a numeric id if no prefix is passed, else
   *  a string id may be returned.
   * @example
   *
   * _.uniqueId('contact_');
   * // => 'contact_104'
   */
  function uniqueId(prefix) {
    var id = idCounter++;
    return prefix ? prefix + id : id;
  }

  /*--------------------------------------------------------------------------*/

  /**
   * A JavaScript micro-templating method, similar to John Resig's implementation.
   * Lo-Dash templating handles arbitrary delimiters, preserves whitespace, and
   * correctly escapes quotes within interpolated code.
   *
   * @static
   * @memberOf _
   * @category Utilities
   * @param {String} text The template text.
   * @param {Obect} data The data object used to populate the text.
   * @param {Object} options The options object.
   * @returns {Function|String} Returns a compiled function when no `data` object
   *  is given, else it returns the interpolated text.
   * @example
   *
   * // using compiled template
   * var compiled = _.template('hello: <%= name %>');
   * compiled({ 'name': 'moe' });
   * // => 'hello: moe'
   *
   * var list = '% _.forEach(people, function(name) { %> <li><%= name %></li> <% }); %>';
   * _.template(list, { 'people': ['moe', 'curly', 'larry'] });
   * // => '<li>moe</li><li>curly</li><li>larry</li>'
   *
   * var template = _.template('<b><%- value %></b>');
   * template({ 'value': '<script>' });
   * // => '<b>&lt;script&gt;</b>'
   *
   * // using `print`
   * var compiled = _.template('<% print("Hello " + epithet); %>');
   * compiled({ 'epithet': 'stooge' });
   * // => 'Hello stooge.'
   *
   * // using custom template settings
   * _.templateSettings = {
   *   'interpolate': /\{\{(.+?)\}\}/g
   * };
   *
   * var template = _.template('Hello {{ name }}!');
   * template({ 'name': 'Mustache' });
   * // => 'Hello Mustache!'
   *
   *
   * // using the `variable` option
   * _.template('<%= data.hasWith %>', { 'hasWith': 'no' }, { 'variable': 'data' });
   * // => 'no'
   *
   * // using the `source` property
   * <script>
   *   JST.project = <%= _.template(jstText).source %>;
   * </script>
   */
  function template(text, data, options) {
    options = defaults(options || {}, lodash.templateSettings);

    // Compile the template source, taking care to escape characters that
    // cannot be included in string literals and then unescape them in code
    // blocks.
    var source = "__p+='" + text
      .replace(reEscaper, function(match) {
        return '\\' + escapes[match];
      })
      .replace(options.escape || reNoMatch, function(match, code) {
        return "'+\n_.escape(" + unescape(code) + ")+\n'";
      })
      .replace(options.interpolate || reNoMatch, function(match, code) {
        return "'+\n(" + unescape(code) + ")+\n'";
      })
      .replace(options.evaluate || reNoMatch, function(match, code) {
        return "';\n" + unescape(code) + ";\n__p+='";
      }) + "';\n";

    // if a variable is not specified, place data values in local scope
    if (!options.variable) {
      source = 'with(object||{}){\n' + source + '\n}\n';
    }

    source = 'var __p="";' +
      'function print(){__p+=Array.prototype.join.call(arguments,"")}\n' +
      source + 'return __p';

    var render = Function(options.variable || 'object', '_', source);
    if (data) {
      return render(data, lodash);
    }

    var template = function(data) {
      return render.call(this, data, lodash);
    };

    // provide the compiled function source as a convenience for build time precompilation
    template.source = 'function(' + (options.variable || 'object') + '){\n' + source + '\n}';

    return template;
  }

  /*--------------------------------------------------------------------------*/

  /**
   * Wraps the value in a `lodash` chainable object.
   *
   * @static
   * @memberOf _
   * @category Chaining
   * @param {Mixed} value The value to wrap.
   * @returns {Object} Returns the `lodash` chainable object.
   * @example
   *
   * var stooges = [
   *   { 'name': 'moe', 'age': 40 },
   *   { 'name': 'larry', 'age': 50 },
   *   { 'name': 'curly', 'age': 60 }
   * ];
   *
   * var youngest = _.chain(stooges)
   *     .sortBy(function(stooge) { return stooge.age; })
   *     .map(function(stooge) { return stooge.name + ' is ' + stooge.age; })
   *     .first()
   *     .value();
   * // => 'moe is 40'
   */
  function chain(value) {
    return new Lodash(value).chain();
  }

  /**
   * Extracts the value from a wrapped chainable object.
   *
   * @name chain
   * @memberOf _
   * @category Chaining
   * @returns {Mixed} Returns the wrapped object.
   * @example
   *
   * _([1, 2, 3]).value();
   * // => [1, 2, 3]
   */
  function chainWrapper() {
    this._chain = true;
    return this;
  }

  /**
   * Extracts the value from a wrapped chainable object.
   *
   * @memberOf _
   * @category Chaining
   * @returns {Mixed} Returns the wrapped object.
   * @example
   *
   * _([1, 2, 3]).value();
   * // => [1, 2, 3]
   */
  function value() {
    return this._wrapped;
  }

  /*--------------------------------------------------------------------------*/

  extend(lodash, {

    /**
     * The semantic version number.
     *
     * @static
     * @memberOf _
     * @type String
     */
    'VERSION': '0.1.0',

    /**
     * By default, Lo-Dash uses ERB-style template delimiters, change the
     * following template settings to use alternative delimiters.
     *
     * @static
     * @memberOf _
     * @type Object
     */
    'templateSettings': {

      /**
       * Used to detect `data` property values to be HTML-escaped.
       *
       * @static
       * @memberOf _.templateSettings
       * @type RegExp
       */
      'escape': /<%-([\s\S]+?)%>/g,

      /**
       * Used to detect code to be evaluated.
       *
       * @static
       * @memberOf _.templateSettings
       * @type RegExp
       */
      'evaluate': /<%([\s\S]+?)%>/g,

      /**
       * Used to detect `data` property values to inject.
       *
       * @static
       * @memberOf _.templateSettings
       * @type RegExp
       */
      'interpolate': /<%=([\s\S]+?)%>/g
    },

    // assign static methods
    'after': after,
    'bind': bind,
    'bindAll': bindAll,
    'chain': chain,
    'clone': clone,
    'compact': compact,
    'compose': compose,
    'contains': contains,
    'debounce': debounce,
    'defaults': defaults,
    'defer': defer,
    'delay': delay,
    'difference': difference,
    'escape': escape,
    'every': every,
    'extend': extend,
    'filter': filter,
    'find': find,
    'first': first,
    'flatten': flatten,
    'forEach': forEach,
    'functions': functions,
    'groupBy': groupBy,
    'has': has,
    'identity': identity,
    'indexOf': indexOf,
    'initial': initial,
    'intersection': intersection,
    'invoke': invoke,
    'isArguments': isArguments,
    'isArray': isArray,
    'isBoolean': isBoolean,
    'isDate': isDate,
    'isElement': isElement,
    'isEmpty': isEmpty,
    'isEqual': isEqual,
    'isFinite': isFinite,
    'isFunction': isFunction,
    'isNaN': isNaN,
    'isNull': isNull,
    'isNumber': isNumber,
    'isObject': isObject,
    'isRegExp': isRegExp,
    'isString': isString,
    'isUndefined': isUndefined,
    'keys': keys,
    'last': last,
    'lastIndexOf': lastIndexOf,
    'map': map,
    'max': max,
    'memoize': memoize,
    'min': min,
    'mixin': mixin,
    'noConflict': noConflict,
    'once': once,
    'pick': pick,
    'pluck': pluck,
    'range': range,
    'reduce': reduce,
    'reduceRight': reduceRight,
    'reject': reject,
    'rest': rest,
    'result': result,
    'shuffle': shuffle,
    'size': size,
    'some': some,
    'sortBy': sortBy,
    'sortedIndex': sortedIndex,
    'tap': tap,
    'template': template,
    'throttle': throttle,
    'times': times,
    'toArray': toArray,
    'union': union,
    'uniq': uniq,
    'uniqueId': uniqueId,
    'values': values,
    'without': without,
    'wrap': wrap,
    'zip': zip,

    // assign aliases
    'all': every,
    'any': some,
    'collect': map,
    'detect': find,
    'each': forEach,
    'foldl': reduce,
    'foldr': reduceRight,
    'head': first,
    'include': contains,
    'inject': reduce,
    'intersect': intersection,
    'methods': functions,
    'select': filter,
    'tail': rest,
    'take': first,
    'unique': uniq
  });

  /*--------------------------------------------------------------------------*/

  // assign private `Lodash` constructor's prototype
  Lodash.prototype = lodash.prototype;

  // add all of the static functions to `Lodash.prototype`
  mixin(lodash);

  // add all mutator Array functions to the wrapper.
  forEach(['pop', 'push', 'reverse', 'shift', 'sort', 'splice', 'unshift'], function(methodName) {
    var func = ArrayProto[methodName];

    lodash.prototype[methodName] = function() {
      var value = this._wrapped;
      func.apply(value, arguments);

      // IE compatibility mode and IE < 9 have buggy Array `shift()` and `splice()`
      // functions that fail to remove the last element, `object[0]`, of
      // array-like-objects even though the `length` property is set to `0`.
      // The `shift()` method is buggy in IE 8 compatibility mode, while `splice()`
      // is buggy regardless of mode in IE < 9 and buggy in compatibility mode in IE 9.
      if (value.length === 0) {
        delete value[0];
      }
      return this._chain ? new Lodash(value).chain() : value;
    };
  });

  // add all accessor Array functions to the wrapper.
  forEach(['concat', 'join', 'slice'], function(methodName) {
    var func = ArrayProto[methodName];
    Lodash.prototype[methodName] = function() {
      var result = func.apply(this._wrapped, arguments);
      return this._chain ? new Lodash(result).chain() : result;
    };
  });

  // add `chain` and `value` after calling to `mixin()` to avoid getting wrapped
  extend(Lodash.prototype, {
    'chain': chainWrapper,
    'value': value
  });

  /*--------------------------------------------------------------------------*/

  // expose lodash
  if (freeExports) {
    // in Node.js or RingoJS v0.8.0+
    if (typeof module == 'object' && module && module.exports == freeExports) {
      (module.exports = lodash)._ = lodash;
    }
    // in Narwhal or RingoJS v0.7.0-
    else {
      freeExports._ = lodash;
    }
  }
  // via an AMD loader
  else if (typeof define == 'function' && typeof define.amd == 'object' && define.amd && define.amd.lodash) {
    define('lodash', function() {
      return lodash;
    });
  }
  // in a browser or Rhino
  else {
    window._ = lodash;
  }
}(this));