lodash/dist/lodash.underscore.js

A utility library delivering consistency, customization, performance, and extras.

/**
 * @license
 * Lo-Dash 1.0.2 (Custom Build) <http://lodash.com/>
 * Build: `lodash underscore -o ./dist/lodash.underscore.js`
 * Copyright 2012-2013 The Dojo Foundation <http://dojofoundation.org/>
 * Based on Underscore.js 1.4.4 <http://underscorejs.org/>
 * Copyright 2009-2013 Jeremy Ashkenas, DocumentCloud Inc.
 * Available under MIT license <http://lodash.com/license>
 */
;(function(window, undefined) {

  /** Detect free variable `exports` */
  var freeExports = typeof exports == 'object' && exports;

  /** Detect free variable `module` */
  var freeModule = typeof module == 'object' && module && module.exports == freeExports && module;

  /** Detect free variable `global` and use it as `window` */
  var freeGlobal = typeof global == 'object' && global;
  if (freeGlobal.global === freeGlobal) {
    window = freeGlobal;
  }

  /** Used for array and object method references */
  var arrayRef = [],
      objectRef = {};

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

  /** Used internally to indicate various things */
  var indicatorObject = objectRef;

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

  /** Used to match HTML entities */
  var reEscapedHtml = /&(?:amp|lt|gt|quot|#39);/g;

  /** Used to match empty string literals in compiled template source */
  var reEmptyStringLeading = /\b__p \+= '';/g,
      reEmptyStringMiddle = /\b(__p \+=) '' \+/g,
      reEmptyStringTrailing = /(__e\(.*?\)|\b__t\)) \+\n'';/g;

  /** Used to match regexp flags from their coerced string values */
  var reFlags = /\w*$/;

  /** Used to detect if a method is native */
  var reNative = RegExp('^' +
    (objectRef.valueOf + '')
      .replace(/[.*+?^${}()|[\]\\]/g, '\\$&')
      .replace(/valueOf|for [^\]]+/g, '.+?') + '$'
  );

  /**
   * Used to match ES6 template delimiters
   * http://people.mozilla.org/~jorendorff/es6-draft.html#sec-7.8.6
   */
  var reEsTemplate = /\$\{([^\\}]*(?:\\.[^\\}]*)*)\}/g;

  /** Used to match "interpolate" template delimiters */
  var reInterpolate = /<%=([\s\S]+?)%>/g;

  /** Used to ensure capturing order of template delimiters */
  var reNoMatch = /($^)/;

  /** Used to match HTML characters */
  var reUnescapedHtml = /[&<>"']/g;

  /** Used to match unescaped characters in compiled string literals */
  var reUnescapedString = /['\n\r\t\u2028\u2029\\]/g;

  /** Used to make template sourceURLs easier to identify */
  var templateCounter = 0;

  /** Native method shortcuts */
  var ceil = Math.ceil,
      concat = arrayRef.concat,
      floor = Math.floor,
      hasOwnProperty = objectRef.hasOwnProperty,
      push = arrayRef.push,
      toString = objectRef.toString;

  /* Native method shortcuts for methods with the same name as other `lodash` methods */
  var nativeBind = reNative.test(nativeBind = slice.bind) && nativeBind,
      nativeIsArray = reNative.test(nativeIsArray = Array.isArray) && nativeIsArray,
      nativeIsFinite = window.isFinite,
      nativeIsNaN = window.isNaN,
      nativeKeys = reNative.test(nativeKeys = Object.keys) && nativeKeys,
      nativeMax = Math.max,
      nativeMin = Math.min,
      nativeRandom = Math.random;

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

  /** Detect various environments */
  var isIeOpera = !!window.attachEvent,
      isV8 = nativeBind && !/\n|true/.test(nativeBind + isIeOpera);

  /* Detect if `Function#bind` exists and is inferred to be fast (all but V8) */
  var isBindFast = nativeBind && !isV8;

  /**
   * Detect if `Array#shift` and `Array#splice` augment array-like objects
   * incorrectly:
   *
   * Firefox < 10, IE compatibility mode, and IE < 9 have buggy Array `shift()`
   * and `splice()` functions that fail to remove the last element, `value[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.
   */
  var hasObjectSpliceBug = (hasObjectSpliceBug = { '0': 1, 'length': 1 },
    arrayRef.splice.call(hasObjectSpliceBug, 0, 1), hasObjectSpliceBug[0]);

  /** Detect if `arguments` objects are `Object` objects (all but Opera < 10.5) */
  var argsAreObjects = arguments.constructor == Object;

  /** Used to determine if values are of the language type Object */
  var objectTypes = {
    'boolean': false,
    'function': true,
    'object': true,
    'number': false,
    'string': false,
    'undefined': false
  };

  /** Used to escape characters for inclusion in compiled string literals */
  var stringEscapes = {
    '\\': '\\',
    "'": "'",
    '\n': 'n',
    '\r': 'r',
    '\t': 't',
    '\u2028': 'u2028',
    '\u2029': 'u2029'
  };

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

  /**
   * Creates a `lodash` object, that wraps the given `value`, to enable method
   * chaining.
   *
   * In addition to Lo-Dash methods, wrappers also have the following `Array` methods:
   * `concat`, `join`, `pop`, `push`, `reverse`, `shift`, `slice`, `sort`, `splice`,
   * and `unshift`
   *
   * The chainable wrapper functions are:
   * `after`, `assign`, `bind`, `bindAll`, `bindKey`, `chain`, `compact`, `compose`,
   * `concat`, `countBy`, `debounce`, `defaults`, `defer`, `delay`, `difference`,
   * `filter`, `flatten`, `forEach`, `forIn`, `forOwn`, `functions`, `groupBy`,
   * `initial`, `intersection`, `invert`, `invoke`, `keys`, `map`, `max`, `memoize`,
   * `merge`, `min`, `object`, `omit`, `once`, `pairs`, `partial`, `partialRight`,
   * `pick`, `pluck`, `push`, `range`, `reject`, `rest`, `reverse`, `shuffle`,
   * `slice`, `sort`, `sortBy`, `splice`, `tap`, `throttle`, `times`, `toArray`,
   * `union`, `uniq`, `unshift`, `values`, `where`, `without`, `wrap`, and `zip`
   *
   * The non-chainable wrapper functions are:
   * `clone`, `cloneDeep`, `contains`, `escape`, `every`, `find`, `has`, `identity`,
   * `indexOf`, `isArguments`, `isArray`, `isBoolean`, `isDate`, `isElement`, `isEmpty`,
   * `isEqual`, `isFinite`, `isFunction`, `isNaN`, `isNull`, `isNumber`, `isObject`,
   * `isPlainObject`, `isRegExp`, `isString`, `isUndefined`, `join`, `lastIndexOf`,
   * `mixin`, `noConflict`, `pop`, `random`, `reduce`, `reduceRight`, `result`,
   * `shift`, `size`, `some`, `sortedIndex`, `template`, `unescape`, and `uniqueId`
   *
   * The wrapper functions `first` and `last` return wrapped values when `n` is
   * passed, otherwise they return unwrapped values.
   *
   * @name _
   * @constructor
   * @category Chaining
   * @param {Mixed} value The value to wrap in a `lodash` instance.
   * @returns {Object} Returns a `lodash` instance.
   */
  function lodash(value) {
    // exit early if already wrapped, even if wrapped by a different `lodash` constructor
    if (value && typeof value == 'object' && value.__wrapped__) {
      return value;
    }
    // allow invoking `lodash` without the `new` operator
    if (!(this instanceof lodash)) {
      return new lodash(value);
    }
    this.__wrapped__ = value;
  }

  /**
   * By default, the template delimiters used by Lo-Dash are similar to those in
   * embedded Ruby (ERB). Change the following template settings to use alternative
   * delimiters.
   *
   * @static
   * @memberOf _
   * @type Object
   */
  lodash.templateSettings = {

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

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

    /**
     * Used to detect `data` property values to inject.
     *
     * @memberOf _.templateSettings
     * @type RegExp
     */
    'interpolate': reInterpolate,

    /**
     * Used to reference the data object in the template text.
     *
     * @memberOf _.templateSettings
     * @type String
     */
    'variable': ''
  };

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

  /**
   * Used by `_.max` and `_.min` as the default `callback` when a given
   * `collection` is a string value.
   *
   * @private
   * @param {String} value The character to inspect.
   * @returns {Number} Returns the code unit of given character.
   */
  function charAtCallback(value) {
    return value.charCodeAt(0);
  }

  /**
   * Used by `sortBy` to compare transformed `collection` values, stable sorting
   * them in ascending order.
   *
   * @private
   * @param {Object} a The object to compare to `b`.
   * @param {Object} b The object to compare to `a`.
   * @returns {Number} Returns the sort order indicator of `1` or `-1`.
   */
  function compareAscending(a, b) {
    var ai = a.index,
        bi = b.index;

    a = a.criteria;
    b = b.criteria;

    // ensure a stable sort in V8 and other engines
    // http://code.google.com/p/v8/issues/detail?id=90
    if (a !== b) {
      if (a > b || typeof a == 'undefined') {
        return 1;
      }
      if (a < b || typeof b == 'undefined') {
        return -1;
      }
    }
    return ai < bi ? -1 : 1;
  }

  /**
   * Creates a function that, when called, invokes `func` with the `this` binding
   * of `thisArg` and prepends any `partialArgs` to the arguments passed to the
   * bound function.
   *
   * @private
   * @param {Function|String} func The function to bind or the method name.
   * @param {Mixed} [thisArg] The `this` binding of `func`.
   * @param {Array} partialArgs An array of arguments to be partially applied.
   * @param {Object} [rightIndicator] Used to indicate partially applying arguments from the right.
   * @returns {Function} Returns the new bound function.
   */
  function createBound(func, thisArg, partialArgs, rightIndicator) {
    var isFunc = isFunction(func),
        isPartial = !partialArgs,
        key = thisArg;

    // juggle arguments
    if (isPartial) {
      partialArgs = thisArg;
    }
    if (!isFunc) {
      thisArg = func;
    }

    function bound() {
      // `Function#bind` spec
      // http://es5.github.com/#x15.3.4.5
      var args = arguments,
          thisBinding = isPartial ? this : thisArg;

      if (!isFunc) {
        func = thisArg[key];
      }
      if (partialArgs.length) {
        args = args.length
          ? (args = slice(args), rightIndicator ? args.concat(partialArgs) : partialArgs.concat(args))
          : partialArgs;
      }
      if (this instanceof bound) {
        // ensure `new bound` is an instance of `bound` and `func`
        noop.prototype = func.prototype;
        thisBinding = new noop;
        noop.prototype = null;

        // mimic the constructor's `return` behavior
        // http://es5.github.com/#x13.2.2
        var result = func.apply(thisBinding, args);
        return isObject(result) ? result : thisBinding;
      }
      return func.apply(thisBinding, args);
    }
    return bound;
  }

  /**
   * Produces a callback bound to an optional `thisArg`. If `func` is a property
   * name, the created callback will return the property value for a given element.
   * If `func` is an object, the created callback will return `true` for elements
   * that contain the equivalent object properties, otherwise it will return `false`.
   *
   * @private
   * @param {Mixed} [func=identity] The value to convert to a callback.
   * @param {Mixed} [thisArg] The `this` binding of the created callback.
   * @param {Number} [argCount=3] The number of arguments the callback accepts.
   * @returns {Function} Returns a callback function.
   */
  function createCallback(func, thisArg, argCount) {
    if (func == null) {
      return identity;
    }
    var type = typeof func;
    if (type != 'function') {
      if (type != 'object') {
        return function(object) {
          return object[func];
        };
      }
      var props = keys(func);
      return function(object) {
        var length = props.length,
            result = false;
        while (length--) {
          if (!(result = object[props[length]] === func[props[length]])) {
            break;
          }
        }
        return result;
      };
    }
    if (typeof thisArg != 'undefined') {
      if (argCount === 1) {
        return function(value) {
          return func.call(thisArg, value);
        };
      }
      if (argCount === 2) {
        return function(a, b) {
          return func.call(thisArg, a, b);
        };
      }
      if (argCount === 4) {
        return function(accumulator, value, index, object) {
          return func.call(thisArg, accumulator, value, index, object);
        };
      }
      return function(value, index, object) {
        return func.call(thisArg, value, index, object);
      };
    }
    return func;
  }

  /**
   * A function compiled to iterate `arguments` objects, arrays, objects, and
   * strings consistenly across environments, executing the `callback` for each
   * element in the `collection`. The `callback` is bound to `thisArg` and invoked
   * with three arguments; (value, index|key, collection). Callbacks may exit
   * iteration early by explicitly returning `false`.
   *
   * @private
   * @type Function
   * @param {Array|Object|String} collection The collection to iterate over.
   * @param {Function} [callback=identity] The function called per iteration.
   * @param {Mixed} [thisArg] The `this` binding of `callback`.
   * @returns {Array|Object|String} Returns `collection`.
   */
  var each = function (collection, callback, thisArg) {
    var index, iterable = collection, result = iterable;
    if (!iterable) return result;
    callback = callback && typeof thisArg == 'undefined' ? callback : createCallback(callback, thisArg);
    var length = iterable.length; index = -1;
    if (typeof length == 'number') {
      while (++index < length) {
        if (callback(iterable[index], index, collection) === indicatorObject) return result
      }
    }
    else {  
      for (index in iterable) {
        if (hasOwnProperty.call(iterable, index)) {    
        if (callback(iterable[index], index, collection) === indicatorObject) return result;    
        }
      }  
    }
  };

  /**
   * Used by `template` to escape characters for inclusion in compiled
   * string literals.
   *
   * @private
   * @param {String} match The matched character to escape.
   * @returns {String} Returns the escaped character.
   */
  function escapeStringChar(match) {
    return '\\' + stringEscapes[match];
  }

  /**
   * Used by `escape` to convert characters to HTML entities.
   *
   * @private
   * @param {String} match The matched character to escape.
   * @returns {String} Returns the escaped character.
   */
  function escapeHtmlChar(match) {
    return htmlEscapes[match];
  }

  /**
   * Checks if `value` is a DOM node in IE < 9.
   *
   * @private
   * @param {Mixed} value The value to check.
   * @returns {Boolean} Returns `true` if the `value` is a DOM node, else `false`.
   */
  function isNode(value) {
    // IE < 9 presents DOM nodes as `Object` objects except they have `toString`
    // methods that are `typeof` "string" and still can coerce nodes to strings
    return typeof value.toString != 'function' && typeof (value + '') == 'string';
  }

  /**
   * A no-operation function.
   *
   * @private
   */
  function noop() {
    // no operation performed
  }

  /**
   * Slices the `collection` from the `start` index up to, but not including,
   * the `end` index.
   *
   * Note: This function is used, instead of `Array#slice`, to support node lists
   * in IE < 9 and to ensure dense arrays are returned.
   *
   * @private
   * @param {Array|Object|String} collection The collection to slice.
   * @param {Number} start The start index.
   * @param {Number} end The end index.
   * @returns {Array} Returns the new array.
   */
  function slice(array, start, end) {
    start || (start = 0);
    if (typeof end == 'undefined') {
      end = array ? array.length : 0;
    }
    var index = -1,
        length = end - start || 0,
        result = Array(length < 0 ? 0 : length);

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

  /**
   * Used by `unescape` to convert HTML entities to characters.
   *
   * @private
   * @param {String} match The matched character to unescape.
   * @returns {String} Returns the unescaped character.
   */
  function unescapeHtmlChar(match) {
    return htmlUnescapes[match];
  }

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

  /**
   * Checks if `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
   */
  function isArguments(value) {
    return toString.call(value) == argsClass;
  }
  // fallback for browsers that can't detect `arguments` objects by [[Class]]
  if (!isArguments(arguments)) {
    isArguments = function(value) {
      return value ? hasOwnProperty.call(value, 'callee') : false;
    };
  }

  /**
   * Iterates over `object`'s own and inherited enumerable properties, executing
   * the `callback` for each property. The `callback` is bound to `thisArg` and
   * invoked with three arguments; (value, key, object). Callbacks may exit iteration
   * early by explicitly returning `false`.
   *
   * @static
   * @memberOf _
   * @type Function
   * @category Objects
   * @param {Object} object The object to iterate over.
   * @param {Function} [callback=identity] The function called per iteration.
   * @param {Mixed} [thisArg] The `this` binding of `callback`.
   * @returns {Object} Returns `object`.
   * @example
   *
   * function Dog(name) {
   *   this.name = name;
   * }
   *
   * Dog.prototype.bark = function() {
   *   alert('Woof, woof!');
   * };
   *
   * _.forIn(new Dog('Dagny'), function(value, key) {
   *   alert(key);
   * });
   * // => alerts 'name' and 'bark' (order is not guaranteed)
   */
  var forIn = function (collection, callback) {
    var index, iterable = collection, result = iterable;
    if (!iterable) return result;
    if (!objectTypes[typeof iterable]) return result;
    callback || (callback = identity);
    
      for (index in iterable) {
        if (callback(iterable[index], index, collection) === indicatorObject) return result;    
      }  
    return result
  };

  /**
   * Iterates over an object's own enumerable properties, executing the `callback`
   * for each property. The `callback` is bound to `thisArg` and invoked with three
   * arguments; (value, key, object). Callbacks may exit iteration early by explicitly
   * returning `false`.
   *
   * @static
   * @memberOf _
   * @type Function
   * @category Objects
   * @param {Object} object The object to iterate over.
   * @param {Function} [callback=identity] The function called per iteration.
   * @param {Mixed} [thisArg] The `this` binding of `callback`.
   * @returns {Object} Returns `object`.
   * @example
   *
   * _.forOwn({ '0': 'zero', '1': 'one', 'length': 2 }, function(num, key) {
   *   alert(key);
   * });
   * // => alerts '0', '1', and 'length' (order is not guaranteed)
   */
  var forOwn = function (collection, callback) {
    var index, iterable = collection, result = iterable;
    if (!iterable) return result;
    if (!objectTypes[typeof iterable]) return result;
    callback || (callback = identity);
    
      for (index in iterable) {
        if (hasOwnProperty.call(iterable, index)) {    
        if (callback(iterable[index], index, collection) === indicatorObject) return result;    
        }
      }  
    return result
  };

  /**
   * Checks if `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(value) {
    // `instanceof` may cause a memory leak in IE 7 if `value` is a host object
    // http://ajaxian.com/archives/working-aroung-the-instanceof-memory-leak
    return (argsAreObjects && value instanceof Array) || toString.call(value) == arrayClass;
  };

  /**
   * Creates an array composed of the own enumerable property names of `object`.
   *
   * @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'] (order is not guaranteed)
   */
  var keys = !nativeKeys ? shimKeys : function(object) {
    if (!isObject(object)) {
      return [];
    }
    return nativeKeys(object);
  };

  /**
   * A fallback implementation of `isPlainObject` that checks if a given `value`
   * is an object created by the `Object` constructor, assuming objects created
   * by the `Object` constructor have no inherited enumerable properties and that
   * there are no `Object.prototype` extensions.
   *
   * @private
   * @param {Mixed} value The value to check.
   * @returns {Boolean} Returns `true`, if `value` is a plain object, else `false`.
   */
  function shimIsPlainObject(value) {
    // avoid non-objects and false positives for `arguments` objects
    var result = false;
    if (!(value && typeof value == 'object') || isArguments(value)) {
      return result;
    }
    // check that the constructor is `Object` (i.e. `Object instanceof Object`)
    var ctor = value.constructor;
    if ((!isFunction(ctor)) || ctor instanceof ctor) {
      // In most environments an object's own properties are iterated before
      // its inherited properties. If the last iterated property is an object's
      // own property then there are no inherited enumerable properties.
      forIn(value, function(value, key) {
        result = key;
      });
      return result === false || hasOwnProperty.call(value, result);
    }
    return result;
  }

  /**
   * A fallback implementation of `Object.keys` that produces an array of the
   * given object's own enumerable property names.
   *
   * @private
   * @param {Object} object The object to inspect.
   * @returns {Array} Returns a new array of property names.
   */
  function shimKeys(object) {
    var result = [];
    forOwn(object, function(value, key) {
      result.push(key);
    });
    return result;
  }

  /**
   * Used to convert characters to HTML entities:
   *
   * Though the `>` character is escaped for symmetry, characters like `>` and `/`
   * don't require escaping in HTML and have no special meaning unless they're part
   * of a tag or an unquoted attribute value.
   * http://mathiasbynens.be/notes/ambiguous-ampersands (under "semi-related fun fact")
   */
  var htmlEscapes = {
    '&': '&amp;',
    '<': '&lt;',
    '>': '&gt;',
    '"': '&quot;',
    "'": '&#39;'
  };

  /** Used to convert HTML entities to characters */
  var htmlUnescapes = invert(htmlEscapes);

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

  /**
   * Assigns own enumerable properties of source object(s) to the destination
   * object. Subsequent sources will overwrite propery assignments of previous
   * sources. If a `callback` function is passed, it will be executed to produce
   * the assigned values. The `callback` is bound to `thisArg` and invoked with
   * two arguments; (objectValue, sourceValue).
   *
   * @static
   * @memberOf _
   * @type Function
   * @alias extend
   * @category Objects
   * @param {Object} object The destination object.
   * @param {Object} [source1, source2, ...] The source objects.
   * @param {Function} [callback] The function to customize assigning values.
   * @param {Mixed} [thisArg] The `this` binding of `callback`.
   * @returns {Object} Returns the destination object.
   * @example
   *
   * _.assign({ 'name': 'moe' }, { 'age': 40 });
   * // => { 'name': 'moe', 'age': 40 }
   *
   * var defaults = _.partialRight(_.assign, function(a, b) {
   *   return typeof a == 'undefined' ? b : a;
   * });
   *
   * var food = { 'name': 'apple' };
   * defaults(food, { 'name': 'banana', 'type': 'fruit' });
   * // => { 'name': 'apple', 'type': 'fruit' }
   */
  function assign(object) {
    if (!object) {
      return object;
    }
    for (var argsIndex = 1, argsLength = arguments.length; argsIndex < argsLength; argsIndex++) {
      var iterable = arguments[argsIndex];
      if (iterable) {
        for (var key in iterable) {
          object[key] = iterable[key];
        }
      }
    }
    return object;
  }

  /**
   * Creates a clone of `value`. If `deep` is `true`, nested objects will also
   * be cloned, otherwise they will be assigned by reference. If a `callback`
   * function is passed, it will be executed to produce the cloned values. If
   * `callback` returns `undefined`, cloning will be handled by the method instead.
   * The `callback` is bound to `thisArg` and invoked with one argument; (value).
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Mixed} value The value to clone.
   * @param {Boolean} [deep=false] A flag to indicate a deep clone.
   * @param {Function} [callback] The function to customize cloning values.
   * @param {Mixed} [thisArg] The `this` binding of `callback`.
   * @param- {Array} [stackA=[]] Internally used to track traversed source objects.
   * @param- {Array} [stackB=[]] Internally used to associate clones with source counterparts.
   * @returns {Mixed} Returns the cloned `value`.
   * @example
   *
   * var stooges = [
   *   { 'name': 'moe', 'age': 40 },
   *   { 'name': 'larry', 'age': 50 }
   * ];
   *
   * var shallow = _.clone(stooges);
   * shallow[0] === stooges[0];
   * // => true
   *
   * var deep = _.clone(stooges, true);
   * deep[0] === stooges[0];
   * // => false
   *
   * _.mixin({
   *   'clone': _.partialRight(_.clone, function(value) {
   *     return _.isElement(value) ? value.cloneNode(false) : undefined;
   *   })
   * });
   *
   * var clone = _.clone(document.body);
   * clone.childNodes.length;
   * // => 0
   */
  function clone(value) {
    return isObject(value)
      ? (isArray(value) ? slice(value) : assign({}, value))
      : value
  }

  /**
   * Assigns own enumerable properties of source object(s) to the destination
   * object for all destination properties that resolve to `undefined`. Once a
   * property is set, additional defaults of the same property will be ignored.
   *
   * @static
   * @memberOf _
   * @type Function
   * @category Objects
   * @param {Object} object The destination object.
   * @param {Object} [source1, source2, ...] The source objects.
   * @param- {Object} [guard] Internally used to allow working with `_.reduce`
   *  without using its callback's `key` and `object` arguments as sources.
   * @returns {Object} Returns the destination object.
   * @example
   *
   * var food = { 'name': 'apple' };
   * _.defaults(food, { 'name': 'banana', 'type': 'fruit' });
   * // => { 'name': 'apple', 'type': 'fruit' }
   */
  function defaults(object) {
    if (!object) {
      return object;
    }
    for (var argsIndex = 1, argsLength = arguments.length; argsIndex < argsLength; argsIndex++) {
      var iterable = arguments[argsIndex];
      if (iterable) {
        for (var key in iterable) {
          if (object[key] == null) {
            object[key] = iterable[key];
          }
        }
      }
    }
    return object;
  }

  /**
   * Creates a sorted array of all enumerable 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', ...]
   */
  function functions(object) {
    var result = [];
    forIn(object, function(value, key) {
      if (isFunction(value)) {
        result.push(key);
      }
    });
    return 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, property) {
    return object ? hasOwnProperty.call(object, property) : false;
  }

  /**
   * Creates an object composed of the inverted keys and values of the given `object`.
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Object} object The object to invert.
   * @returns {Object} Returns the created inverted object.
   * @example
   *
   *  _.invert({ 'first': 'moe', 'second': 'larry' });
   * // => { 'moe': 'first', 'larry': 'second' } (order is not guaranteed)
   */
  function invert(object) {
    var index = -1,
        props = keys(object),
        length = props.length,
        result = {};

    while (++index < length) {
      var key = props[index];
      result[object[key]] = key;
    }
    return result;
  }

  /**
   * Checks if `value` is a boolean 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 `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 value instanceof Date || toString.call(value) == dateClass;
  }

  /**
   * Checks if `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 : false;
  }

  /**
   * Checks if `value` is empty. Arrays, strings, or `arguments` objects with a
   * length of `0` and objects with no own enumerable properties are considered
   * "empty".
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Array|Object|String} value The value to inspect.
   * @returns {Boolean} Returns `true`, if the `value` is empty, else `false`.
   * @example
   *
   * _.isEmpty([1, 2, 3]);
   * // => false
   *
   * _.isEmpty({});
   * // => true
   *
   * _.isEmpty('');
   * // => true
   */
  function isEmpty(value) {
    if (!value) {
      return true;
    }
    if (isArray(value) || isString(value)) {
      return !value.length;
    }
    for (var key in value) {
      if (hasOwnProperty.call(value, key)) {
        return false;
      }
    }
    return true;
  }

  /**
   * Performs a deep comparison between two values to determine if they are
   * equivalent to each other. If `callback` is passed, it will be executed to
   * compare values. If `callback` returns `undefined`, comparisons will be handled
   * by the method instead. The `callback` is bound to `thisArg` and invoked with
   * two arguments; (a, b).
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Mixed} a The value to compare.
   * @param {Mixed} b The other value to compare.
   * @param {Function} [callback] The function to customize comparing values.
   * @param {Mixed} [thisArg] The `this` binding of `callback`.
   * @param- {Object} [stackA=[]] Internally used track traversed `a` objects.
   * @param- {Object} [stackB=[]] Internally used track traversed `b` objects.
   * @returns {Boolean} Returns `true`, if the values are equvalent, else `false`.
   * @example
   *
   * var moe = { 'name': 'moe', 'age': 40 };
   * var copy = { 'name': 'moe', 'age': 40 };
   *
   * moe == copy;
   * // => false
   *
   * _.isEqual(moe, copy);
   * // => true
   *
   * var words = ['hello', 'goodbye'];
   * var otherWords = ['hi', 'goodbye'];
   *
   * _.isEqual(words, otherWords, function(a, b) {
   *   var reGreet = /^(?:hello|hi)$/i,
   *       aGreet = _.isString(a) && reGreet.test(a),
   *       bGreet = _.isString(b) && reGreet.test(b);
   *
   *   return (aGreet || bGreet) ? (aGreet == bGreet) : undefined;
   * });
   * // => true
   */
  function isEqual(a, b, stackA, stackB) {
    if (a === b) {
      return a !== 0 || (1 / a == 1 / b);
    }
    var type = typeof a,
        otherType = typeof b;

    if (a === a &&
        (!a || (type != 'function' && type != 'object')) &&
        (!b || (otherType != 'function' && otherType != 'object'))) {
      return false;
    }
    if (a == null || b == null) {
      return a === b;
    }
    var className = toString.call(a),
        otherClass = toString.call(b);

    if (className != otherClass) {
      return false;
    }
    switch (className) {
      case boolClass:
      case dateClass:
        return +a == +b;

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

      case regexpClass:
      case stringClass:
        return a == b + '';
    }
    var isArr = className == arrayClass;
    if (!isArr) {
      if (a.__wrapped__ || b.__wrapped__) {
        return isEqual(a.__wrapped__ || a, b.__wrapped__ || b, stackA, stackB);
      }
      if (className != objectClass) {
        return false;
      }
      var ctorA = a.constructor,
          ctorB = b.constructor;

      if (ctorA != ctorB && !(
            isFunction(ctorA) && ctorA instanceof ctorA &&
            isFunction(ctorB) && ctorB instanceof ctorB
          )) {
        return false;
      }
    }
    stackA || (stackA = []);
    stackB || (stackB = []);

    var length = stackA.length;
    while (length--) {
      if (stackA[length] == a) {
        return stackB[length] == b;
      }
    }
    var result = true,
        size = 0;

    stackA.push(a);
    stackB.push(b);

    if (isArr) {
      size = b.length;
      result = size == a.length;

      if (result) {
        while (size--) {
          if (!(result = isEqual(a[size], b[size], stackA, stackB))) {
            break;
          }
        }
      }
      return result;
    }
    forIn(b, function(value, key, b) {
      if (hasOwnProperty.call(b, key)) {
        size++;
        return !(result = hasOwnProperty.call(a, key) && isEqual(a[key], value, stackA, stackB)) && indicatorObject;
      }
    });

    if (result) {
      forIn(a, function(value, key, a) {
        if (hasOwnProperty.call(a, key)) {
          return !(result = --size > -1) && indicatorObject;
        }
      });
    }
    return result;
  }

  /**
   * Checks if `value` is, or can be coerced to, a finite number.
   *
   * Note: This is not the same as native `isFinite`, which will return true for
   * booleans and empty strings. See http://es5.github.com/#x15.1.2.5.
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Mixed} value The value to check.
   * @returns {Boolean} Returns `true`, if the `value` is finite, else `false`.
   * @example
   *
   * _.isFinite(-101);
   * // => true
   *
   * _.isFinite('10');
   * // => true
   *
   * _.isFinite(true);
   * // => false
   *
   * _.isFinite('');
   * // => false
   *
   * _.isFinite(Infinity);
   * // => false
   */
  function isFinite(value) {
    return nativeIsFinite(value) && !nativeIsNaN(parseFloat(value));
  }

  /**
   * Checks if `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(_);
   * // => true
   */
  function isFunction(value) {
    return typeof value == 'function';
  }
  // fallback for older versions of Chrome and Safari
  if (isFunction(/x/)) {
    isFunction = function(value) {
      return value instanceof Function || toString.call(value) == funcClass;
    };
  }

  /**
   * Checks if `value` is the language type of Object.
   * (e.g. arrays, functions, objects, regexes, `new Number(0)`, and `new String('')`)
   *
   * @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, 2, 3]);
   * // => true
   *
   * _.isObject(1);
   * // => false
   */
  function isObject(value) {
    // check if the value is the ECMAScript language type of Object
    // http://es5.github.com/#x8
    // and avoid a V8 bug
    // http://code.google.com/p/v8/issues/detail?id=2291
    return value ? objectTypes[typeof value] : false;
  }

  /**
   * Checks if `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
    // (perform the [[Class]] check first to avoid errors with some host objects in IE)
    return isNumber(value) && value != +value
  }

  /**
   * Checks if `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 `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 typeof value == 'number' || toString.call(value) == numberClass;
  }

  /**
   * Checks if `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 value instanceof RegExp || toString.call(value) == regexpClass;
  }

  /**
   * Checks if `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 typeof value == 'string' || toString.call(value) == stringClass;
  }

  /**
   * Checks if `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 typeof value == 'undefined';
  }

  /**
   * Creates a shallow clone of `object` excluding the specified properties.
   * Property names may be specified as individual arguments or as arrays of
   * property names. If a `callback` function is passed, it will be executed
   * for each property in the `object`, omitting the properties `callback`
   * returns truthy for. The `callback` is bound to `thisArg` and invoked
   * with three arguments; (value, key, object).
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Object} object The source object.
   * @param {Function|String} callback|[prop1, prop2, ...] The properties to omit
   *  or the function called per iteration.
   * @param {Mixed} [thisArg] The `this` binding of `callback`.
   * @returns {Object} Returns an object without the omitted properties.
   * @example
   *
   * _.omit({ 'name': 'moe', 'age': 40 }, 'age');
   * // => { 'name': 'moe' }
   *
   * _.omit({ 'name': 'moe', 'age': 40 }, function(value) {
   *   return typeof value == 'number';
   * });
   * // => { 'name': 'moe' }
   */
  function omit(object) {
    var props = concat.apply(arrayRef, arguments),
        result = {};

    forIn(object, function(value, key) {
      if (indexOf(props, key, 1) < 0) {
        result[key] = value;
      }
    });
    return result;
  }

  /**
   * Creates a two dimensional array of the given object's key-value pairs,
   * i.e. `[[key1, value1], [key2, value2]]`.
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Object} object The object to inspect.
   * @returns {Array} Returns new array of key-value pairs.
   * @example
   *
   * _.pairs({ 'moe': 30, 'larry': 40 });
   * // => [['moe', 30], ['larry', 40]] (order is not guaranteed)
   */
  function pairs(object) {
    var index = -1,
        props = keys(object),
        length = props.length,
        result = Array(length);

    while (++index < length) {
      var key = props[index];
      result[index] = [key, object[key]];
    }
    return result;
  }

  /**
   * Creates a shallow clone of `object` composed of the specified properties.
   * Property names may be specified as individual arguments or as arrays of property
   * names. If `callback` is passed, it will be executed for each property in the
   * `object`, picking the properties `callback` returns truthy for. The `callback`
   * is bound to `thisArg` and invoked with three arguments; (value, key, object).
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Object} object The source object.
   * @param {Array|Function|String} callback|[prop1, prop2, ...] The function called
   *  per iteration or properties to pick, either as individual arguments or arrays.
   * @param {Mixed} [thisArg] The `this` binding of `callback`.
   * @returns {Object} Returns an object composed of the picked properties.
   * @example
   *
   * _.pick({ 'name': 'moe', '_userid': 'moe1' }, 'name');
   * // => { 'name': 'moe' }
   *
   * _.pick({ 'name': 'moe', '_userid': 'moe1' }, function(value, key) {
   *   return key.charAt(0) != '_';
   * });
   * // => { 'name': 'moe' }
   */
  function pick(object) {
    var index = 0,
        props = concat.apply(arrayRef, arguments),
        length = props.length,
        result = {};

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

  /**
   * Creates an array composed of the own enumerable property values of `object`.
   *
   * @static
   * @memberOf _
   * @category Objects
   * @param {Object} object The object to inspect.
   * @returns {Array} Returns a new array of property values.
   * @example
   *
   * _.values({ 'one': 1, 'two': 2, 'three': 3 });
   * // => [1, 2, 3]
   */
  function values(object) {
    var index = -1,
        props = keys(object),
        length = props.length,
        result = Array(length);

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

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

  /**
   * Checks if a given `target` element is present in a `collection` using strict
   * equality for comparisons, i.e. `===`. If `fromIndex` is negative, it is used
   * as the offset from the end of the collection.
   *
   * @static
   * @memberOf _
   * @alias include
   * @category Collections
   * @param {Array|Object|String} collection The collection to iterate over.
   * @param {Mixed} target The value to check for.
   * @param {Number} [fromIndex=0] The index to search from.
   * @returns {Boolean} Returns `true` if the `target` element is found, else `false`.
   * @example
   *
   * _.contains([1, 2, 3], 1);
   * // => true
   *
   * _.contains([1, 2, 3], 1, 2);
   * // => false
   *
   * _.contains({ 'name': 'moe', 'age': 40 }, 'moe');
   * // => true
   *
   * _.contains('curly', 'ur');
   * // => true
   */
  function contains(collection, target) {
    var length = collection ? collection.length : 0,
        result = false;
    if (typeof length == 'number') {
      result = indexOf(collection, target) > -1;
    } else {
      each(collection, function(value) {
        return (result = value === target) && indicatorObject;
      });
    }
    return result;
  }

  /**
   * Creates an object composed of keys returned from running each element of the
   * `collection` through the given `callback`. The corresponding value of each key
   * is the number of times the key was returned by the `callback`. The `callback`
   * is bound to `thisArg` and invoked with three arguments; (value, index|key, collection).
   *
   * If a property name is passed for `callback`, the created "_.pluck" style
   * callback will return the property value of the given element.
   *
   * If an object is passed for `callback`, the created "_.where" style callback
   * will return `true` for elements that have the propeties of the given object,
   * else `false`.
   *
   * @static
   * @memberOf _
   * @category Collections
   * @param {Array|Object|String} collection The collection to iterate over.
   * @param {Function|Object|String} [callback=identity] The function called per
   *  iteration. If a property name or object is passed, it will be used to create
   *  a "_.pluck" or "_.where" style callback, respectively.
   * @param {Mixed} [thisArg] The `this` binding of `callback`.
   * @returns {Object} Returns the composed aggregate object.
   * @example
   *
   * _.countBy([4.3, 6.1, 6.4], function(num) { return Math.floor(num); });
   * // => { '4': 1, '6': 2 }
   *
   * _.countBy([4.3, 6.1, 6.4], function(num) { return this.floor(num); }, Math);
   * // => { '4': 1, '6': 2 }
   *
   * _.countBy(['one', 'two', 'three'], 'length');
   * // => { '3': 2, '5': 1 }
   */
  function countBy(collection, callback, thisArg) {
    var result = {};
    callback = createCallback(callback, thisArg);

    forEach(collection, function(value, key, collection) {
      key = callback(value, key, collection) + '';
      (hasOwnProperty.call(result, key) ? result[key]++ : result[key] = 1);
    });
    return result;
  }

  /**
   * Checks if the `callback` returns a truthy value for **all** elements of a
   * `collection`. The `callback` is bound to `thisArg` and invoked with three
   * arguments; (value, index|key, collection).
   *
   * If a property name is passed for `callback`, the created "_.pluck" style
   * callback will return the property value of the given element.
   *
   * If an object is passed for `callback`, the created "_.where" style callback
   * will return `true` for elements that have the propeties of the given object,
   * else `false`.
   *
   * @static
   * @memberOf _
   * @alias all
   * @category Collections
   * @param {Array|Object|String} collection The collection to iterate over.
   * @param {Function|Object|String} [callback=identity] The function called per
   *  iteration. If a property name or object is passed, it will be used to create
   *  a "_.pluck" or "_.where" style callback, respectively.
   * @param {Mixed} [thisArg] The `this` binding of `callback`.
   * @returns {Boolean} Returns `true` if all elements pass the callback check,
   *  else `false`.
   * @example
   *
   * _.every([true, 1, null, 'yes'], Boolean);
   * // => false
   *
   * var stooges = [
   *   { 'name': 'moe', 'age': 40 },
   *   { 'name': 'larry', 'age': 50 }
   * ];
   *
   * // using "_.pluck" callback shorthand
   * _.every(stooges, 'age');
   * // => true
   *
   * // using "_.where" callback shorthand
   * _.every(stooges, { 'age': 50 });
   * // => false
   */
  function every(collection, callback, thisArg) {
    var result = true;
    callback = createCallback(callback, thisArg);

    if (isArray(collection)) {
      var index = -1,
          length = collection.length;

      while (++index < length) {
        if (!(result = !!callback(collection[index], index, collection))) {
          break;
        }
      }
    } else {
      each(collection, function(value, i