_.dropRightWhile(array, [predicate=_.identity])

9

_.dropRightWhile(array, [predicate=_.identity])

建立一個數組的切片，從結尾丟棄掉一些元素。被丟棄的元素是從結尾開始循環，直到predicate返回了false。predicate函數有三個參數，value，index，array。

參數

array (Array): 須要建立切片的數組
[predicate=_.identity] (Function): 遍歷調用的方法

返回值

(Array): 返回一個新數組切片

例子

var users = [
  { 'user': 'barney',  'active': true },
  { 'user': 'fred',    'active': false },
  { 'user': 'pebbles', 'active': false }
];
 
_.dropRightWhile(users, function(o) { return !o.active; });
// => objects for ['barney']
 
// The `_.matches` iteratee shorthand.
_.dropRightWhile(users, { 'user': 'pebbles', 'active': false });
// => objects for ['barney', 'fred']
 
// The `_.matchesProperty` iteratee shorthand.
_.dropRightWhile(users, ['active', false]);
// => objects for ['barney']
 
// The `_.property` iteratee shorthand.
_.dropRightWhile(users, 'active');
// => objects for ['barney', 'fred', 'pebbles']

源代碼：

/**
 * lodash (Custom Build) <https://lodash.com/>
 * Build: `lodash modularize exports="npm" -o ./`
 * Copyright jQuery Foundation and other contributors <https://jquery.org/>
 * Released under MIT license <https://lodash.com/license>
 * Based on Underscore.js 1.8.3 <http://underscorejs.org/LICENSE>
 * Copyright Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
 */

/** Used as the size to enable large array optimizations. */
var LARGE_ARRAY_SIZE = 200;

/** Used as the `TypeError` message for "Functions" methods. */
var FUNC_ERROR_TEXT = 'Expected a function';

/** Used to stand-in for `undefined` hash values. */
var HASH_UNDEFINED = '__lodash_hash_undefined__';

/** Used to compose bitmasks for comparison styles. */
var UNORDERED_COMPARE_FLAG = 1,
    PARTIAL_COMPARE_FLAG = 2;

/** Used as references for various `Number` constants. */
var INFINITY = 1 / 0,
    MAX_SAFE_INTEGER = 9007199254740991;

/** `Object#toString` result references. */
var argsTag = '[object Arguments]',
    arrayTag = '[object Array]',
    boolTag = '[object Boolean]',
    dateTag = '[object Date]',
    errorTag = '[object Error]',
    funcTag = '[object Function]',
    genTag = '[object GeneratorFunction]',
    mapTag = '[object Map]',
    numberTag = '[object Number]',
    objectTag = '[object Object]',
    promiseTag = '[object Promise]',
    regexpTag = '[object RegExp]',
    setTag = '[object Set]',
    stringTag = '[object String]',
    symbolTag = '[object Symbol]',
    weakMapTag = '[object WeakMap]';

var arrayBufferTag = '[object ArrayBuffer]',
    dataViewTag = '[object DataView]',
    float32Tag = '[object Float32Array]',
    float64Tag = '[object Float64Array]',
    int8Tag = '[object Int8Array]',
    int16Tag = '[object Int16Array]',
    int32Tag = '[object Int32Array]',
    uint8Tag = '[object Uint8Array]',
    uint8ClampedTag = '[object Uint8ClampedArray]',
    uint16Tag = '[object Uint16Array]',
    uint32Tag = '[object Uint32Array]';

/** Used to match property names within property paths. */
var reIsDeepProp = /\.|\[(?:[^[\]]*|(["'])(?:(?!\1)[^\\]|\\.)*?\1)\]/,
    reIsPlainProp = /^\w*$/,
    reLeadingDot = /^\./,
    rePropName = /[^.[\]]+|\[(?:(-?\d+(?:\.\d+)?)|(["'])((?:(?!\2)[^\\]|\\.)*?)\2)\]|(?=(?:\.|\[\])(?:\.|\[\]|$))/g;

/**
 * Used to match `RegExp`
 * [syntax characters](http://ecma-international.org/ecma-262/7.0/#sec-patterns).
 */
var reRegExpChar = /[\\^$.*+?()[\]{}|]/g;

/** Used to match backslashes in property paths. */
var reEscapeChar = /\\(\\)?/g;

/** Used to detect host constructors (Safari). */
var reIsHostCtor = /^\[object .+?Constructor\]$/;

/** Used to detect unsigned integer values. */
var reIsUint = /^(?:0|[1-9]\d*)$/;

/** Used to identify `toStringTag` values of typed arrays. */
var typedArrayTags = {};
typedArrayTags[float32Tag] = typedArrayTags[float64Tag] =
typedArrayTags[int8Tag] = typedArrayTags[int16Tag] =
typedArrayTags[int32Tag] = typedArrayTags[uint8Tag] =
typedArrayTags[uint8ClampedTag] = typedArrayTags[uint16Tag] =
typedArrayTags[uint32Tag] = true;
typedArrayTags[argsTag] = typedArrayTags[arrayTag] =
typedArrayTags[arrayBufferTag] = typedArrayTags[boolTag] =
typedArrayTags[dataViewTag] = typedArrayTags[dateTag] =
typedArrayTags[errorTag] = typedArrayTags[funcTag] =
typedArrayTags[mapTag] = typedArrayTags[numberTag] =
typedArrayTags[objectTag] = typedArrayTags[regexpTag] =
typedArrayTags[setTag] = typedArrayTags[stringTag] =
typedArrayTags[weakMapTag] = false;

/** Detect free variable `global` from Node.js. */
var freeGlobal = typeof global == 'object' && global && global.Object === Object && global;

/** Detect free variable `self`. */
var freeSelf = typeof self == 'object' && self && self.Object === Object && self;

/** Used as a reference to the global object. */
var root = freeGlobal || freeSelf || Function('return this')();

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

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

/** Detect the popular CommonJS extension `module.exports`. */
var moduleExports = freeModule && freeModule.exports === freeExports;

/** Detect free variable `process` from Node.js. */
var freeProcess = moduleExports && freeGlobal.process;

/** Used to access faster Node.js helpers. */
var nodeUtil = (function() {
  try {
    return freeProcess && freeProcess.binding('util');
  } catch (e) {}
}());

/* Node.js helper references. */
var nodeIsTypedArray = nodeUtil && nodeUtil.isTypedArray;

/**
 * A specialized version of `_.some` for arrays without support for iteratee
 * shorthands.
 *
 * @private
 * @param {Array} [array] The array to iterate over.
 * @param {Function} predicate The function invoked per iteration.
 * @returns {boolean} Returns `true` if any element passes the predicate check,
 *  else `false`.
 */
function arraySome(array, predicate) {
  var index = -1,
      length = array ? array.length : 0;

  while (++index < length) {
    if (predicate(array[index], index, array)) {
      return true;
    }
  }
  return false;
}

/**
 * The base implementation of `_.property` without support for deep paths.
 *
 * @private
 * @param {string} key The key of the property to get.
 * @returns {Function} Returns the new accessor function.
 */
//返回一個方法，這個方法返回object的對應key的對應value
function baseProperty(key) {
  return function(object) {
    return object == null ? undefined : object[key];
  };
}

/**
 * The base implementation of `_.times` without support for iteratee shorthands
 * or max array length checks.
 *
 * @private
 * @param {number} n The number of times to invoke `iteratee`.
 * @param {Function} iteratee The function invoked per iteration.
 * @returns {Array} Returns the array of results.
 */
//_times的基礎實現，返回一個長度爲n的數組，元素值是遍歷器處理過的index
//n是循環調用遍歷器的次數，iteratee是遍歷器
function baseTimes(n, iteratee) {
  var index = -1,//循環索引
      result = Array(n);//結果數組

  while (++index < n) {
    result[index] = iteratee(index);
  }
  return result;
}

/**
 * The base implementation of `_.unary` without support for storing metadata.
 *
 * @private
 * @param {Function} func The function to cap arguments for.
 * @returns {Function} Returns the new capped function.
 */
//_.unary的基礎實現，建立一個函數只接受一個參數，忽略以後全部參數
function baseUnary(func) {
  return function(value) {
    return func(value);
  };
}

/**
 * Gets the value at `key` of `object`.
 *
 * @private
 * @param {Object} [object] The object to query.
 * @param {string} key The key of the property to get.
 * @returns {*} Returns the property value.
 */
function getValue(object, key) {
  return object == null ? undefined : object[key];
}

/**
 * Checks if `value` is a host object in IE < 9.
 *
 * @private
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is a host object, else `false`.
 */
//檢查一個值是不是宿主對象，在小於IE9的瀏覽器狀況下，例如BOM和DOM對象
function isHostObject(value) {
  // Many host objects are `Object` objects that can coerce to strings
  // despite having improperly defined `toString` methods.
  //不少宿主對象能夠強制轉換成字符串儘管它們的toString方法定義並不正確
  var result = false;
  if (value != null && typeof value.toString != 'function') {
    try {
      result = !!(value + '');
    } catch (e) {}
  }
  return result;
}

/**
 * Converts `map` to its key-value pairs.
 *
 * @private
 * @param {Object} map The map to convert.
 * @returns {Array} Returns the key-value pairs.
 */
//將本身實現的兼容式map數據類型轉變成key-value形式
function mapToArray(map) {
  var index = -1,//循環索引
      result = Array(map.size);//結果數組

  map.forEach(function(value, key) {//循環賦值
    /*
    {key1: value1, key2: value2, ...}
    變成：
    [[key1, value1], [key2, value2], ...]
    */
    result[++index] = [key, value];
  });
  return result;
}

/**
 * Creates a unary function that invokes `func` with its argument transformed.
 *
 * @private
 * @param {Function} func The function to wrap.
 * @param {Function} transform The argument transform.
 * @returns {Function} Returns the new function.
 */
function overArg(func, transform) {
  return function(arg) {
    return func(transform(arg));
  };
}

/**
 * Converts `set` to an array of its values.
 *
 * @private
 * @param {Object} set The set to convert.
 * @returns {Array} Returns the values.
 */
function setToArray(set) {
  var index = -1,
      result = Array(set.size);

  set.forEach(function(value) {
    result[++index] = value;
  });
  return result;
}

/** Used for built-in method references. */
var arrayProto = Array.prototype,
    funcProto = Function.prototype,
    objectProto = Object.prototype;

/** Used to detect overreaching core-js shims. */
var coreJsData = root['__core-js_shared__'];

/** Used to detect methods masquerading as native. */
var maskSrcKey = (function() {
  var uid = /[^.]+$/.exec(coreJsData && coreJsData.keys && coreJsData.keys.IE_PROTO || '');
  return uid ? ('Symbol(src)_1.' + uid) : '';
}());

/** Used to resolve the decompiled source of functions. */
var funcToString = funcProto.toString;

/** Used to check objects for own properties. */
var hasOwnProperty = objectProto.hasOwnProperty;

/**
 * Used to resolve the
 * [`toStringTag`](http://ecma-international.org/ecma-262/7.0/#sec-object.prototype.tostring)
 * of values.
 */
var objectToString = objectProto.toString;

/** Used to detect if a method is native. */
var reIsNative = RegExp('^' +
  funcToString.call(hasOwnProperty).replace(reRegExpChar, '\\$&')
  .replace(/hasOwnProperty|(function).*?(?=\\\()| for .+?(?=\\\])/g, '$1.*?') + '$'
);

/** Built-in value references. */
var Symbol = root.Symbol,
    Uint8Array = root.Uint8Array,
    propertyIsEnumerable = objectProto.propertyIsEnumerable,
    splice = arrayProto.splice;

/* Built-in method references for those with the same name as other `lodash` methods. */
var nativeKeys = overArg(Object.keys, Object);

/* Built-in method references that are verified to be native. */
var DataView = getNative(root, 'DataView'),
    Map = getNative(root, 'Map'),
    Promise = getNative(root, 'Promise'),
    Set = getNative(root, 'Set'),
    WeakMap = getNative(root, 'WeakMap'),
    nativeCreate = getNative(Object, 'create');

/** Used to detect maps, sets, and weakmaps. */
var dataViewCtorString = toSource(DataView),
    mapCtorString = toSource(Map),
    promiseCtorString = toSource(Promise),
    setCtorString = toSource(Set),
    weakMapCtorString = toSource(WeakMap);

/** Used to convert symbols to primitives and strings. */
var symbolProto = Symbol ? Symbol.prototype : undefined,
    symbolValueOf = symbolProto ? symbolProto.valueOf : undefined,
    symbolToString = symbolProto ? symbolProto.toString : undefined;

/**
 * Creates a hash object.
 *
 * @private
 * @constructor
 * @param {Array} [entries] The key-value pairs to cache.
 */
function Hash(entries) {
  var index = -1,
      length = entries ? entries.length : 0;

  this.clear();
  while (++index < length) {
    var entry = entries[index];
    this.set(entry[0], entry[1]);
  }
}

/**
 * Removes all key-value entries from the hash.
 *
 * @private
 * @name clear
 * @memberOf Hash
 */
function hashClear() {
  this.__data__ = nativeCreate ? nativeCreate(null) : {};
}

/**
 * Removes `key` and its value from the hash.
 *
 * @private
 * @name delete
 * @memberOf Hash
 * @param {Object} hash The hash to modify.
 * @param {string} key The key of the value to remove.
 * @returns {boolean} Returns `true` if the entry was removed, else `false`.
 */
function hashDelete(key) {
  return this.has(key) && delete this.__data__[key];
}

/**
 * Gets the hash value for `key`.
 *
 * @private
 * @name get
 * @memberOf Hash
 * @param {string} key The key of the value to get.
 * @returns {*} Returns the entry value.
 */
function hashGet(key) {
  var data = this.__data__;
  if (nativeCreate) {
    var result = data[key];
    return result === HASH_UNDEFINED ? undefined : result;
  }
  return hasOwnProperty.call(data, key) ? data[key] : undefined;
}

/**
 * Checks if a hash value for `key` exists.
 *
 * @private
 * @name has
 * @memberOf Hash
 * @param {string} key The key of the entry to check.
 * @returns {boolean} Returns `true` if an entry for `key` exists, else `false`.
 */
function hashHas(key) {
  var data = this.__data__;
  return nativeCreate ? data[key] !== undefined : hasOwnProperty.call(data, key);
}

/**
 * Sets the hash `key` to `value`.
 *
 * @private
 * @name set
 * @memberOf Hash
 * @param {string} key The key of the value to set.
 * @param {*} value The value to set.
 * @returns {Object} Returns the hash instance.
 */
function hashSet(key, value) {
  var data = this.__data__;
  data[key] = (nativeCreate && value === undefined) ? HASH_UNDEFINED : value;
  return this;
}

// Add methods to `Hash`.
Hash.prototype.clear = hashClear;
Hash.prototype['delete'] = hashDelete;
Hash.prototype.get = hashGet;
Hash.prototype.has = hashHas;
Hash.prototype.set = hashSet;

/**
 * Creates an list cache object.
 *
 * @private
 * @constructor
 * @param {Array} [entries] The key-value pairs to cache.
 */
function ListCache(entries) {
  var index = -1,
      length = entries ? entries.length : 0;

  this.clear();
  while (++index < length) {
    var entry = entries[index];
    this.set(entry[0], entry[1]);
  }
}

/**
 * Removes all key-value entries from the list cache.
 *
 * @private
 * @name clear
 * @memberOf ListCache
 */
function listCacheClear() {
  this.__data__ = [];
}

/**
 * Removes `key` and its value from the list cache.
 *
 * @private
 * @name delete
 * @memberOf ListCache
 * @param {string} key The key of the value to remove.
 * @returns {boolean} Returns `true` if the entry was removed, else `false`.
 */
function listCacheDelete(key) {
  var data = this.__data__,
      index = assocIndexOf(data, key);

  if (index < 0) {
    return false;
  }
  var lastIndex = data.length - 1;
  if (index == lastIndex) {
    data.pop();
  } else {
    splice.call(data, index, 1);
  }
  return true;
}

/**
 * Gets the list cache value for `key`.
 *
 * @private
 * @name get
 * @memberOf ListCache
 * @param {string} key The key of the value to get.
 * @returns {*} Returns the entry value.
 */
function listCacheGet(key) {
  var data = this.__data__,
      index = assocIndexOf(data, key);

  return index < 0 ? undefined : data[index][1];
}

/**
 * Checks if a list cache value for `key` exists.
 *
 * @private
 * @name has
 * @memberOf ListCache
 * @param {string} key The key of the entry to check.
 * @returns {boolean} Returns `true` if an entry for `key` exists, else `false`.
 */
function listCacheHas(key) {
  return assocIndexOf(this.__data__, key) > -1;
}

/**
 * Sets the list cache `key` to `value`.
 *
 * @private
 * @name set
 * @memberOf ListCache
 * @param {string} key The key of the value to set.
 * @param {*} value The value to set.
 * @returns {Object} Returns the list cache instance.
 */
function listCacheSet(key, value) {
  var data = this.__data__,
      index = assocIndexOf(data, key);

  if (index < 0) {
    data.push([key, value]);
  } else {
    data[index][1] = value;
  }
  return this;
}

// Add methods to `ListCache`.
ListCache.prototype.clear = listCacheClear;
ListCache.prototype['delete'] = listCacheDelete;
ListCache.prototype.get = listCacheGet;
ListCache.prototype.has = listCacheHas;
ListCache.prototype.set = listCacheSet;

/**
 * Creates a map cache object to store key-value pairs.
 *
 * @private
 * @constructor
 * @param {Array} [entries] The key-value pairs to cache.
 */
function MapCache(entries) {
  var index = -1,
      length = entries ? entries.length : 0;

  this.clear();
  while (++index < length) {
    var entry = entries[index];
    this.set(entry[0], entry[1]);
  }
}

/**
 * Removes all key-value entries from the map.
 *
 * @private
 * @name clear
 * @memberOf MapCache
 */
function mapCacheClear() {
  this.__data__ = {
    'hash': new Hash,
    'map': new (Map || ListCache),
    'string': new Hash
  };
}

/**
 * Removes `key` and its value from the map.
 *
 * @private
 * @name delete
 * @memberOf MapCache
 * @param {string} key The key of the value to remove.
 * @returns {boolean} Returns `true` if the entry was removed, else `false`.
 */
function mapCacheDelete(key) {
  return getMapData(this, key)['delete'](key);
}

/**
 * Gets the map value for `key`.
 *
 * @private
 * @name get
 * @memberOf MapCache
 * @param {string} key The key of the value to get.
 * @returns {*} Returns the entry value.
 */
function mapCacheGet(key) {
  return getMapData(this, key).get(key);
}

/**
 * Checks if a map value for `key` exists.
 *
 * @private
 * @name has
 * @memberOf MapCache
 * @param {string} key The key of the entry to check.
 * @returns {boolean} Returns `true` if an entry for `key` exists, else `false`.
 */
function mapCacheHas(key) {
  return getMapData(this, key).has(key);
}

/**
 * Sets the map `key` to `value`.
 *
 * @private
 * @name set
 * @memberOf MapCache
 * @param {string} key The key of the value to set.
 * @param {*} value The value to set.
 * @returns {Object} Returns the map cache instance.
 */
function mapCacheSet(key, value) {
  getMapData(this, key).set(key, value);
  return this;
}

// Add methods to `MapCache`.
MapCache.prototype.clear = mapCacheClear;
MapCache.prototype['delete'] = mapCacheDelete;
MapCache.prototype.get = mapCacheGet;
MapCache.prototype.has = mapCacheHas;
MapCache.prototype.set = mapCacheSet;

/**
 *
 * Creates an array cache object to store unique values.
 *
 * @private
 * @constructor
 * @param {Array} [values] The values to cache.
 */
function SetCache(values) {
  var index = -1,
      length = values ? values.length : 0;

  this.__data__ = new MapCache;
  while (++index < length) {
    this.add(values[index]);
  }
}

/**
 * Adds `value` to the array cache.
 *
 * @private
 * @name add
 * @memberOf SetCache
 * @alias push
 * @param {*} value The value to cache.
 * @returns {Object} Returns the cache instance.
 */
function setCacheAdd(value) {
  this.__data__.set(value, HASH_UNDEFINED);
  return this;
}

/**
 * Checks if `value` is in the array cache.
 *
 * @private
 * @name has
 * @memberOf SetCache
 * @param {*} value The value to search for.
 * @returns {number} Returns `true` if `value` is found, else `false`.
 */
function setCacheHas(value) {
  return this.__data__.has(value);
}

// Add methods to `SetCache`.
SetCache.prototype.add = SetCache.prototype.push = setCacheAdd;
SetCache.prototype.has = setCacheHas;

/**
 * Creates a stack cache object to store key-value pairs.
 *
 * @private
 * @constructor
 * @param {Array} [entries] The key-value pairs to cache.
 */
function Stack(entries) {
  this.__data__ = new ListCache(entries);
}

/**
 * Removes all key-value entries from the stack.
 *
 * @private
 * @name clear
 * @memberOf Stack
 */
function stackClear() {
  this.__data__ = new ListCache;
}

/**
 * Removes `key` and its value from the stack.
 *
 * @private
 * @name delete
 * @memberOf Stack
 * @param {string} key The key of the value to remove.
 * @returns {boolean} Returns `true` if the entry was removed, else `false`.
 */
function stackDelete(key) {
  return this.__data__['delete'](key);
}

/**
 * Gets the stack value for `key`.
 *
 * @private
 * @name get
 * @memberOf Stack
 * @param {string} key The key of the value to get.
 * @returns {*} Returns the entry value.
 */
function stackGet(key) {
  return this.__data__.get(key);
}

/**
 * Checks if a stack value for `key` exists.
 *
 * @private
 * @name has
 * @memberOf Stack
 * @param {string} key The key of the entry to check.
 * @returns {boolean} Returns `true` if an entry for `key` exists, else `false`.
 */
function stackHas(key) {
  return this.__data__.has(key);
}

/**
 * Sets the stack `key` to `value`.
 *
 * @private
 * @name set
 * @memberOf Stack
 * @param {string} key The key of the value to set.
 * @param {*} value The value to set.
 * @returns {Object} Returns the stack cache instance.
 */
function stackSet(key, value) {
  var cache = this.__data__;
  if (cache instanceof ListCache) {
    var pairs = cache.__data__;
    if (!Map || (pairs.length < LARGE_ARRAY_SIZE - 1)) {
      pairs.push([key, value]);
      return this;
    }
    cache = this.__data__ = new MapCache(pairs);
  }
  cache.set(key, value);
  return this;
}

// Add methods to `Stack`.
Stack.prototype.clear = stackClear;
Stack.prototype['delete'] = stackDelete;
Stack.prototype.get = stackGet;
Stack.prototype.has = stackHas;
Stack.prototype.set = stackSet;

/**
 * Creates an array of the enumerable property names of the array-like `value`.
 *
 * @private
 * @param {*} value The value to query.
 * @param {boolean} inherited Specify returning inherited property names.
 * @returns {Array} Returns the array of property names.
 */
//建立一個包含一個array-like對象的全部自身可枚舉屬性的key的數組
function arrayLikeKeys(value, inherited) {
  // Safari 8.1 makes `arguments.callee` enumerable in strict mode.
  // Safari 9 makes `arguments.length` enumerable in strict mode.
  var result = (isArray(value) || isArguments(value))
    ? baseTimes(value.length, String)
    : [];
//結果數組，若是value是array或者arguments對象，調用baseTimes返回一個結果數組，元素是String化的索引值
  var length = result.length,//結果數組長度
      skipIndexes = !!length;

  for (var key in value) {//循環value對象
    if ((inherited || hasOwnProperty.call(value, key)) &&
        !(skipIndexes && (key == 'length' || isIndex(key, length)))) {
          //若是除了索引屬性和length屬性以外還有其餘屬性，加入結果數組
      result.push(key);
    }
  }
  return result;
}

/**
 * Gets the index at which the `key` is found in `array` of key-value pairs.
 *
 * @private
 * @param {Array} array The array to inspect.
 * @param {*} key The key to search for.
 * @returns {number} Returns the index of the matched value, else `-1`.
 */
function assocIndexOf(array, key) {
  var length = array.length;
  while (length--) {
    if (eq(array[length][0], key)) {
      return length;
    }
  }
  return -1;
}

/**
 * The base implementation of `_.get` without support for default values.
 *
 * @private
 * @param {Object} object The object to query.
 * @param {Array|string} path The path of the property to get.
 * @returns {*} Returns the resolved value.
 */
//根據path獲取object上的屬性值
//object須要獲取屬性值的對象
//path屬性所在的路徑
function baseGet(object, path) {
  path = isKey(path, object) ? [path] : castPath(path);
  //判斷path是否是合法屬性名，若是是就存成[path]，若是不是就調用castPath方法生成path的數組

  var index = 0,//循環索引
      length = path.length;//path數組的長度

  while (object != null && index < length) {//獲取深層的值
    object = object[toKey(path[index++])];
  }
  return (index && index == length) ? object : undefined;//找到就返回，沒找到返回undefined
}

/**
 * The base implementation of `getTag`.
 *
 * @private
 * @param {*} value The value to query.
 * @returns {string} Returns the `toStringTag`.
 */
//調用Object.prototype.toString得到數據的類型tag
function baseGetTag(value) {
  return objectToString.call(value);
}

/**
 * The base implementation of `_.hasIn` without support for deep paths.
 *
 * @private
 * @param {Object} [object] The object to query.
 * @param {Array|string} key The key to check.
 * @returns {boolean} Returns `true` if `key` exists, else `false`.
 */
function baseHasIn(object, key) {
  return object != null && key in Object(object);
}

/**
 * The base implementation of `_.isEqual` which supports partial comparisons
 * and tracks traversed objects.
 *
 * @private
 * @param {*} value The value to compare.
 * @param {*} other The other value to compare.
 * @param {Function} [customizer] The function to customize comparisons.
 * @param {boolean} [bitmask] The bitmask of comparison flags.
 *  The bitmask may be composed of the following flags:
 *     1 - Unordered comparison
 *     2 - Partial comparison
 * @param {Object} [stack] Tracks traversed `value` and `other` objects.
 * @returns {boolean} Returns `true` if the values are equivalent, else `false`.
 */
//_.isEqual的基礎實現，深度比較兩個對象是不是相等的
//value要比較的對象，other要比較的另外一個對象，customizer自定義比較方法
//bitmask爲1說明是無序的比較，爲2說明是部分比較
//stack追蹤傳入的參數
function baseIsEqual(value, other, customizer, bitmask, stack) {
  if (value === other) {//若是value和other嚴格相等，直接返回true
    return true;
  }
  if (value == null || other == null || (!isObject(value) && !isObjectLike(other))) {
    //判斷有值爲空或者NaN，反正不是數組或對象的狀況的狀況
    return value !== value && other !== other;
  }
  return baseIsEqualDeep(value, other, baseIsEqual, customizer, bitmask, stack);
  //調用baseIsEqualDeep來判斷
}

/**
 * A specialized version of `baseIsEqual` for arrays and objects which performs
 * deep comparisons and tracks traversed objects enabling objects with circular
 * references to be compared.
 *
 * @private
 * @param {Object} object The object to compare.
 * @param {Object} other The other object to compare.
 * @param {Function} equalFunc The function to determine equivalents of values.
 * @param {Function} [customizer] The function to customize comparisons.
 * @param {number} [bitmask] The bitmask of comparison flags. See `baseIsEqual`
 *  for more details.
 * @param {Object} [stack] Tracks traversed `object` and `other` objects.
 * @returns {boolean} Returns `true` if the objects are equivalent, else `false`.
 */
//深度比較數組和對象是否相等
function baseIsEqualDeep(object, other, equalFunc, customizer, bitmask, stack) {
  var objIsArr = isArray(object),//判斷object是否是數組
      othIsArr = isArray(other),//判斷other是否是數組
      objTag = arrayTag,//'[object Array]'
      othTag = arrayTag;//'[object Array]'

  if (!objIsArr) {
    objTag = getTag(object);
    objTag = objTag == argsTag ? objectTag : objTag;
  }
  if (!othIsArr) {
    othTag = getTag(other);//若是object不是數組，就獲取object的數據類型tag
    othTag = othTag == argsTag ? objectTag : othTag;
  }
  var objIsObj = objTag == objectTag && !isHostObject(object),//object是對象類型且不是宿主對象
      othIsObj = othTag == objectTag && !isHostObject(other),//other是對象類型且不是宿主對象
      isSameTag = objTag == othTag;//object和other的類型tag同樣

  if (isSameTag && !objIsObj) {//object和other的tag相等且它們不是本地對象類型
    stack || (stack = new Stack);//新建一個ListCache類型數據，ListCache其實就是一個本身實現的Map數據類型
    return (objIsArr || isTypedArray(object))
      ? equalArrays(object, other, equalFunc, customizer, bitmask, stack)
      : equalByTag(object, other, objTag, equalFunc, customizer, bitmask, stack);
      //若是都是數組類型或者typedArray類型就調用equalArrays方法判斷
      //不然調用equalByTag判斷
  }
  if (!(bitmask & PARTIAL_COMPARE_FLAG)) {//若是不是部分比較，且是object類型
    //此處__warpped__屬性看不明白???
    var objIsWrapped = objIsObj && hasOwnProperty.call(object, '__wrapped__'),
        othIsWrapped = othIsObj && hasOwnProperty.call(other, '__wrapped__');

    if (objIsWrapped || othIsWrapped) {
      var objUnwrapped = objIsWrapped ? object.value() : object,
          othUnwrapped = othIsWrapped ? other.value() : other;

      stack || (stack = new Stack);
      return equalFunc(objUnwrapped, othUnwrapped, customizer, bitmask, stack);//遞歸調用baseIsEqual
    }
  }
  if (!isSameTag) {//若是toStringTag不同，直接返回false
    return false;
  }
  stack || (stack = new Stack);
  return equalObjects(object, other, equalFunc, customizer, bitmask, stack);
  //其餘狀況使用equalObjects來判斷
}

/**
 * The base implementation of `_.isMatch` without support for iteratee shorthands.
 *
 * @private
 * @param {Object} object The object to inspect.
 * @param {Object} source The object of property values to match.
 * @param {Array} matchData The property names, values, and compare flags to match.
 * @param {Function} [customizer] The function to customize comparisons.
 * @returns {boolean} Returns `true` if `object` is a match, else `false`.
 */
//object，給定對象
//source，用來比較的源對象
//matchData，source參數的[key, value, boolean]的數組的形式，第三個布爾值代表當前值是否適合用===比較
//自定義比較函數
function baseIsMatch(object, source, matchData, customizer) {
  var index = matchData.length,//循環索引，從結尾開始循環
      length = index,//source長度
      noCustomizer = !customizer;//有沒有傳遞自定義比較方法的標識

  if (object == null) {//若是object爲空，若source有屬性，返回false，若source無屬性，返回true
    return !length;
  }
  object = Object(object);//強制轉換object
  while (index--) {//按source屬性長度循環
    var data = matchData[index];//當前matchData
    if ((noCustomizer && data[2])
          ? data[1] !== object[data[0]]
          : !(data[0] in object)
        ) {//若是沒有自定義比較方法且當前source屬性值適合===判斷，也就是說是簡單類型數據，就直接用!==判斷是否不相等
          //不然用in來判斷object是否不含有source key屬性
      return false;
    }
  }
  //上面循環先循環一遍判斷適合使用===直接判斷的屬性，下面循環再循環一遍判斷其餘須要深度循環判斷的屬性
  //上面循環結束後index循環索引變成0，如今再次正向循環
  while (++index < length) {
    data = matchData[index];//當前matchData
    var key = data[0],//當前source key
        objValue = object[key],//當前object 對應source key 的值
        srcValue = data[1];//當前source value

    if (noCustomizer && data[2]) {//若是沒有自定義比較方法，且是簡單類型，就判斷objValue上是否不存在此屬性
      //若是不存在直接返回false
      if (objValue === undefined && !(key in object)) {
        return false;
      }
    } else {
      var stack = new Stack;//新實例化一個Stack對象
      if (customizer) {//若是有自定義比較方法，就用自定義的比較
        var result = customizer(objValue, srcValue, key, object, source, stack);
      }
      if (!(result === undefined
            ? baseIsEqual(srcValue, objValue, customizer, UNORDERED_COMPARE_FLAG | PARTIAL_COMPARE_FLAG, stack)
            : result
          )) {//若是沒有自定義比較方法，就用baseIsEqual來比較
        return false;
      }
    }
  }
  return true;
}

/**
 * The base implementation of `_.isNative` without bad shim checks.
 *
 * @private
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is a native function,
 *  else `false`.
 */
function baseIsNative(value) {
  if (!isObject(value) || isMasked(value)) {
    return false;
  }
  var pattern = (isFunction(value) || isHostObject(value)) ? reIsNative : reIsHostCtor;
  return pattern.test(toSource(value));
}

/**
 * The base implementation of `_.isTypedArray` without Node.js optimizations.
 *
 * @private
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is a typed array, else `false`.
 */
function baseIsTypedArray(value) {
  return isObjectLike(value) &&
    isLength(value.length) && !!typedArrayTags[objectToString.call(value)];
}

/**
 * The base implementation of `_.iteratee`.
 *
 * @private
 * @param {*} [value=_.identity] The value to convert to an iteratee.
 * @returns {Function} Returns the iteratee.
 */
//_.iteratee的基礎實現，把一個值轉換成一個迭代器函數
function baseIteratee(value) {
  // Don't store the `typeof` result in a variable to avoid a JIT bug in Safari 9.
  // See https://bugs.webkit.org/show_bug.cgi?id=156034 for more details.
  if (typeof value == 'function') {//若是value原本就是function，直接返回
    return value;
  }
  if (value == null) {//若是value是空，迭代器就使用事先定義好的identity方法
    //identity方法返回原值，不作操做
    return identity;
  }
  if (typeof value == 'object') {//若是value是對象
    return isArray(value)
      ? baseMatchesProperty(value[0], value[1])
      : baseMatches(value);
      //若是value是一個數組，調用baseMatchesProperty，則value[0]是path，獲取對象上的屬性的路徑；value[1]是srcValue，和以後傳入參數根據路徑獲取到的屬性值比較用的值，baseMatchesProperty會返回一個方法，這個方法判斷value[1]是否和傳入的對象根據value[0]路徑獲取到的屬性 是相等的，內部比較使用相似baseIsEqual的深層比較方法。相等返回true，不然false
      //若是value的類型不是一個數組，是一個對象，那麼調用baseMatches，baseMatches建立一個方法，這個方法會使用部分的（partial）深度比較來比較給定的對象和source對象，若是給定對象擁有相等的屬性值，就返回true,不然false。這裏給baseMatches傳入的value參數就是source，以後differenctBy循環的時候全部值都會和source比較
  }
  return property(value);
  //若是value都不是以上狀況，那就調用property,建立一個方法，這個方法能夠根據給定path屬性路徑返回給定對象的屬性值
}

/**
 * The base implementation of `_.keys` which doesn't treat sparse arrays as dense.
 *
 * @private
 * @param {Object} object The object to query.
 * @returns {Array} Returns the array of property names.
 */
//_.keys的基礎實現，將對象的可枚舉屬性的key組成一個數組返回
function baseKeys(object) {
  if (!isPrototype(object)) {//若是不是prototype對象，使用原生Object.keys方法
    return nativeKeys(object);
  }
  var result = [];//結果數組
  for (var key in Object(object)) {
    if (hasOwnProperty.call(object, key) && key != 'constructor') {
      //不等於constructor的自身屬性push入結果數組
      result.push(key);
    }
  }
  return result;
}

/**
 * The base implementation of `_.matches` which doesn't clone `source`.
 *
 * @private
 * @param {Object} source The object of property values to match.
 * @returns {Function} Returns the new spec function.
 */
//_.matches方法的基礎實現
//建立一個方法，這個方法會使用部分的（partial）深度比較來比較給定的對象和source對象，若是給定對象擁有相等的屬性值，就返回true,不然false
function baseMatches(source) {
  var matchData = getMatchData(source);
  //getMatchData，把對象變成[key, value, boolean]的數組的形式，第三個布爾值代表當前值是否適合用===比較
  if (matchData.length == 1 && matchData[0][2]) {//若是source對象只有一個屬性
    return matchesStrictComparable(matchData[0][0], matchData[0][1]);
    //matchesStrictComparable返回一個方法，這個方法用於比較傳入對象object key值對應的值是否和給定值srcValue相等
    //matchData[0][0]就是key，matchData[0][1]就是srcValue
  }
  return function(object) {
    //若是source有多個屬性，那麼就調用baseIsMatch
    return object === source || baseIsMatch(object, source, matchData);
  };
}

/**
 * The base implementation of `_.matchesProperty` which doesn't clone `srcValue`.
 *
 * @private
 * @param {string} path The path of the property to get.
 * @param {*} srcValue The value to match.
 * @returns {Function} Returns the new spec function.
 */
//生成一個函數，這個函數能夠深度比較對象的某個屬性是否與給定值相等
//path參數是想要獲取的屬性的路徑
//srcValue是用來匹配的值
function baseMatchesProperty(path, srcValue) {
  if (isKey(path) && isStrictComparable(srcValue)) {
    //若是path是屬性名 而且 srcValue能夠適用嚴格等於===來比較
    return matchesStrictComparable(toKey(path), srcValue);
    //返回一個返回object[key] === srcValue判斷結果的函數
  }
  return function(object) {
    var objValue = get(object, path);//根據path獲取object上對應健的值
    return (objValue === undefined && objValue === srcValue)
      ? hasIn(object, path)
      : baseIsEqual(srcValue, objValue, undefined, UNORDERED_COMPARE_FLAG | PARTIAL_COMPARE_FLAG);
      //返回布爾值，判斷根據path獲取到的值和給定值是否相等
      //若是獲取到的值和用來比較的值都是undefined，那就object中是否存在這個path路徑
      //hasIn判斷path路徑在給定object中是否存在
      //不然用baseIsEqual判斷
  };
}

/**
 * A specialized version of `baseProperty` which supports deep paths.
 *
 * @private
 * @param {Array|string} path The path of the property to get.
 * @returns {Function} Returns the new accessor function.
 */
//返回一個方法，這個方法根據path返回object的對應屬性值
function basePropertyDeep(path) {
  return function(object) {
    return baseGet(object, path);
  };
}

/**
 * The base implementation of `_.slice` without an iteratee call guard.
 *
 * @private
 * @param {Array} array The array to slice.
 * @param {number} [start=0] The start position.
 * @param {number} [end=array.length] The end position.
 * @returns {Array} Returns the slice of `array`.
 */
//建立一個數組array的切片，從起始索引到結束索引，不包括結束索引
function baseSlice(array, start, end) {
  var index = -1,//循環索引
      length = array.length;//數組長度

  if (start < 0) {//起始索引是負數處理，是負數就至關於從末尾往開頭數，也就是和lengh相加
    start = -start > length ? 0 : (length + start);//和length相加後若是仍是小於0就等於0
  }
  end = end > length ? length : end;//結束索引若是大於length就讓它等於length
  if (end < 0) {//處理結束索引是負數
    end += length;
  }
  length = start > end ? 0 : ((end - start) >>> 0);//根據start和end計算這個切片的長度，若是起始在結束後面那麼切片長度爲0，不然相減而且取整
  start >>>= 0;//start取整

  var result = Array(length);//結果切片數組
  while (++index < length) {//循環切片長度的次數，給結果數組每一項賦值
    result[index] = array[index + start];
  }
  return result;
}

/**
 * The base implementation of `_.toString` which doesn't convert nullish
 * values to empty strings.
 *
 * @private
 * @param {*} value The value to process.
 * @returns {string} Returns the string.
 */
//轉換一個值爲字符串，不會處理空值
function baseToString(value) {
  // Exit early for strings to avoid a performance hit in some environments.
  if (typeof value == 'string') {//若是已是字符串，直接返回
    return value;
  }
  if (isSymbol(value)) {//若是是Symbol對象，調用Symbol.prototype.toString處理
    return symbolToString ? symbolToString.call(value) : '';
  }
  var result = (value + '');//隱式轉換
  return (result == '0' && (1 / value) == -INFINITY) ? '-0' : result;//處理-0的狀況
}

/**
 * The base implementation of methods like `_.dropWhile` and `_.takeWhile`
 * without support for iteratee shorthands.
 *
 * @private
 * @param {Array} array The array to query.
 * @param {Function} predicate The function invoked per iteration.
 * @param {boolean} [isDrop] Specify dropping elements instead of taking them.
 * @param {boolean} [fromRight] Specify iterating from right to left.
 * @returns {Array} Returns the slice of `array`.
 */
//dropWhile的基礎實現
//array須要處理的數組，predicate遍歷器函數，isDrop指定丟棄或者獲取元素，fromRight指定循環的方向
function baseWhile(array, predicate, isDrop, fromRight) {
  var length = array.length,//數組的長度
      index = fromRight ? length : -1;//循環索引，若是fromRight爲true，從右往左循環，起始索引是數組長度；若是fromRight爲false，從左往右循環，起始索引是-1

  while ((fromRight ? index-- : ++index < length) &&
    predicate(array[index], index, array)) {}
    //循環數組，length--從右往左循環，-1++從左往右循環
    //爲數組循環值調用predicate，直到predicate返回false，循環索引index後面slice的時候有用
  return isDrop
    ? baseSlice(array, (fromRight ? 0 : index), (fromRight ? index + 1 : length))
    : baseSlice(array, (fromRight ? index + 1 : 0), (fromRight ? length : index));
    //isDrop爲true的時候，若是從右往左丟棄，起始slice爲0，結束slice爲index+1；若是從左往右丟棄，起始slice爲index，結束slice爲length
    //isDrop爲false的時候，若是從右往左獲取，起始slice爲index+1，結束slice爲length；若是從左往右獲取，起始slice爲0，結束slice爲index
}

/**
 * Casts `value` to a path array if it's not one.
 *
 * @private
 * @param {*} value The value to inspect.
 * @returns {Array} Returns the cast property path array.
 */
//把一個.分隔的path值轉換成一個path數組
function castPath(value) {
  return isArray(value) ? value : stringToPath(value);
  //若是path值已是數組了，直接返回；若是不是調用stringToPath方法轉換
}

/**
 * A specialized version of `baseIsEqualDeep` for arrays with support for
 * partial deep comparisons.
 *
 * @private
 * @param {Array} array The array to compare.
 * @param {Array} other The other array to compare.
 * @param {Function} equalFunc The function to determine equivalents of values.
 * @param {Function} customizer The function to customize comparisons.
 * @param {number} bitmask The bitmask of comparison flags. See `baseIsEqual`
 *  for more details.
 * @param {Object} stack Tracks traversed `array` and `other` objects.
 * @returns {boolean} Returns `true` if the arrays are equivalent, else `false`.
 */
//深度比較數組是否相等
//partical部分比較的意思就是，other的長度能夠比array長，other在包含array全部元素的狀況下，還能夠有本身的獨特於array的元素
function equalArrays(array, other, equalFunc, customizer, bitmask, stack) {
  //bitmask內部使用的時候值只能是1或2，1表明無序比較，2表明部分比較
  //bitmask按位與後，只有按位與操做符兩邊數字相等的狀況下才會返回整數，不然返回0
  var isPartial = bitmask & PARTIAL_COMPARE_FLAG,//是否部分比較
      arrLength = array.length,//array長度
      othLength = other.length;//other長度

  if (arrLength != othLength && !(isPartial && othLength > arrLength)) {//長度不符合要求，直接返回false
    return false;
  }
  // Assume cyclic values are equal.
  //一開始先假設循環值都是相等的
  //stack默認是listCache對象，是本身實現的Map數據類型
  var stacked = stack.get(array);//獲取stack上的array key對應的value
  if (stacked && stack.get(other)) {//若是stack key存在，就和other key比較
    return stacked == other;
  }
  var index = -1,//循環索引
      result = true,//一開始先假設循環值都是相等的
      //若是是無序比較，就實例化一個SetCache對象
      seen = (bitmask & UNORDERED_COMPARE_FLAG) ? new SetCache : undefined;

  stack.set(array, other);//給stack裏存上array和other，交叉存
  stack.set(other, array);

  // Ignore non-index properties.
  while (++index < arrLength) {//循環array的長度
    var arrValue = array[index],//當前循環的array值
        othValue = other[index];//當前循環的other值

    if (customizer) {//若是提供了customizer比較方法，就用它來比較，partial部分比較要反過來傳遞array和other
      var compared = isPartial
        ? customizer(othValue, arrValue, index, other, array, stack)
        : customizer(arrValue, othValue, index, array, other, stack);
    }
    if (compared !== undefined) {//若是自定義比較有告終果，且爲真，就continue繼續下一次循環，不然result=false，跳出循環
      if (compared) {
        continue;
      }
      result = false;
      break;
    }
    // Recursively compare arrays (susceptible to call stack limits).
    //遞歸地比較數組元素值是否相等
    if (seen) {//若是建立了seen變量，說明是無序比較
      //seen是SetCache對象，也是利用key-value形式存儲值
      //遍歷other，若是有值和當前array的值相等，就存入seen中，而且arraySome返回true，不然返回false跳出循環
      if (!arraySome(other, function(othValue, othIndex) {
            if (!seen.has(othIndex) &&
                (arrValue === othValue || equalFunc(arrValue, othValue, customizer, bitmask, stack))) {
              return seen.add(othIndex);
            }
          })) {
        result = false;
        break;
      }
    } else if (!(
          arrValue === othValue ||
            equalFunc(arrValue, othValue, customizer, bitmask, stack)
        )) {//其餘狀況比較
      result = false;
      break;
    }
  }
  stack['delete'](array);//stack上刪除array和other屬性
  stack['delete'](other);
  return result;
}

/**
 * A specialized version of `baseIsEqualDeep` for comparing objects of
 * the same `toStringTag`.
 *
 * **Note:** This function only supports comparing values with tags of
 * `Boolean`, `Date`, `Error`, `Number`, `RegExp`, or `String`.
 *
 * @private
 * @param {Object} object The object to compare.
 * @param {Object} other The other object to compare.
 * @param {string} tag The `toStringTag` of the objects to compare.
 * @param {Function} equalFunc The function to determine equivalents of values.
 * @param {Function} customizer The function to customize comparisons.
 * @param {number} bitmask The bitmask of comparison flags. See `baseIsEqual`
 *  for more details.
 * @param {Object} stack Tracks traversed `object` and `other` objects.
 * @returns {boolean} Returns `true` if the objects are equivalent, else `false`.
 */
//比較toStringTag相等的兩個對象是否相等
//object用來比較的對象
//other用來比較的另外一個對象
//tag比較對象的toStringTag
//equalFunc基礎比較相等方法，用來遞歸調用
//customizer自定義比較方法
//bitmask是否無序比較或者部分比較的標誌
//stack，key-value結構跟蹤比較的對象
function equalByTag(object, other, tag, equalFunc, customizer, bitmask, stack) {
  switch (tag) {//根據toStringTag來比較object和other對象
    case dataViewTag:
    //'[object DataView]'
      if ((object.byteLength != other.byteLength) ||
          (object.byteOffset != other.byteOffset)) {
        return false;
      }
      object = object.buffer;
      other = other.buffer;

    case arrayBufferTag:
    //'[object ArrayBuffer]'
      if ((object.byteLength != other.byteLength) ||
          !equalFunc(new Uint8Array(object), new Uint8Array(other))) {
        return false;
      }
      return true;

    case boolTag:
    //'[object Boolean]'
    case dateTag:
    //'[object Date]'
    case numberTag:
    //'[object Number]'
      // Coerce booleans to `1` or `0` and dates to milliseconds.
      // Invalid dates are coerced to `NaN`.
      //強制轉換布爾值到1或0，時間對象轉換爲毫秒，無效的時間轉換爲NaN
      return eq(+object, +other);

    case errorTag:
    //'[object Error]'
      return object.name == other.name && object.message == other.message;

    case regexpTag:
    //'[object RegExp]'
    case stringTag:
    //'[object String]'
      // Coerce regexes to strings and treat strings, primitives and objects,
      // as equal. See http://www.ecma-international.org/ecma-262/7.0/#sec-regexp.prototype.tostring
      // for more details.
      return object == (other + '');

    case mapTag:
    //'[object Map]'
      var convert = mapToArray;
      //將map轉換成數組的方法
      /*
    {key1: value1, key2: value2, ...}
    變成：
    [[key1, value1], [key2, value2], ...]
    */
    case setTag:
    //'[object Set]'
      var isPartial = bitmask & PARTIAL_COMPARE_FLAG;//是否部分比較
      convert || (convert = setToArray);//將map或者set轉換成數組的方法，mapToArray或者setToArray

      if (object.size != other.size && !isPartial) {//若是不是部分比較，且長度不同，直接返回false
        return false;
      }
      // Assume cyclic values are equal.
      //假設循環值都相等，從中判斷不相等的狀況
      var stacked = stack.get(object);
      if (stacked) {
        return stacked == other;
      }
      bitmask |= UNORDERED_COMPARE_FLAG;

      // Recursively compare objects (susceptible to call stack limits).
      stack.set(object, other);//在stack裏把object和other都存上
      var result = equalArrays(convert(object), convert(other), equalFunc, customizer, bitmask, stack);
      //把object和other都轉換成數組，而後用equalArrays方法來比較是否相等
      stack['delete'](object);//清除stack
      return result;

    case symbolTag:
    //'[object Symbol]'
      if (symbolValueOf) {//Symbol.prototype.valueOf
        return symbolValueOf.call(object) == symbolValueOf.call(other);
      }
  }
  return false;
}

/**
 * A specialized version of `baseIsEqualDeep` for objects with support for
 * partial deep comparisons.
 *
 * @private
 * @param {Object} object The object to compare.
 * @param {Object} other The other object to compare.
 * @param {Function} equalFunc The function to determine equivalents of values.
 * @param {Function} customizer The function to customize comparisons.
 * @param {number} bitmask The bitmask of comparison flags. See `baseIsEqual`
 *  for more details.
 * @param {Object} stack Tracks traversed `object` and `other` objects.
 * @returns {boolean} Returns `true` if the objects are equivalent, else `false`.
 */
//判斷object類型深度比較是否相等，支持部分比較
function equalObjects(object, other, equalFunc, customizer, bitmask, stack) {
  var isPartial = bitmask & PARTIAL_COMPARE_FLAG,//是否部分比較
      objProps = keys(object),//Object.keys()，返回key組成的數組
      objLength = objProps.length,
      othProps = keys(other),//Object.keys()，返回key組成的數組
      othLength = othProps.length;

  if (objLength != othLength && !isPartial) {//若是不是部分比較，且object和other的key長度不同，返回false
    return false;
  }
  var index = objLength;//循環索引是object key數組的長度
  while (index--) {
    var key = objProps[index];//object 的key
    if (!(isPartial ? key in other : hasOwnProperty.call(other, key))) {
      //若是是部分比較，就用in來判斷，不然用Object.prototype.hasOwnProperty
      //判斷object的key是否other裏也有
      //若是沒有，返回false
      return false;
    }
  }
  // Assume cyclic values are equal.
  var stacked = stack.get(object);
  if (stacked && stack.get(other)) {
    return stacked == other;
  }
  var result = true;//開始循環以前假設循環的值都是相等的
  stack.set(object, other);
  stack.set(other, object);

  var skipCtor = isPartial;//部分比較，跳過constructor
  while (++index < objLength) {//循環
    key = objProps[index];//object的key
    var objValue = object[key],//object key對應的value
        othValue = other[key];//other key對應的value

    if (customizer) {//若是有自定義比較方法，就用自定義的比較
      var compared = isPartial
        ? customizer(othValue, objValue, key, other, object, stack)
        : customizer(objValue, othValue, key, object, other, stack);
    }
    // Recursively compare objects (susceptible to call stack limits).
    if (!(compared === undefined
          ? (objValue === othValue || equalFunc(objValue, othValue, customizer, bitmask, stack))
          : compared
        )) {
          //若是自定義比較失敗就跳出循環，result=false
          //若是不是自定義比較，就用===比較，或者繼續遞歸調用baseIsEqual來深度比較
      result = false;
      break;
    }
    skipCtor || (skipCtor = key == 'constructor');
  }
  if (result && !skipCtor) {//不是部分比較且object中有constructor屬性，不跳過constructor屬性，判斷constructor是否同樣
    var objCtor = object.constructor,
        othCtor = other.constructor;

    // Non `Object` object instances with different constructors are not equal.
    if (objCtor != othCtor &&
        ('constructor' in object && 'constructor' in other) &&
        !(typeof objCtor == 'function' && objCtor instanceof objCtor &&
          typeof othCtor == 'function' && othCtor instanceof othCtor)) {
      result = false;
    }
  }
  stack['delete'](object);
  stack['delete'](other);
  return result;
}

/**
 * Gets the data for `map`.
 *
 * @private
 * @param {Object} map The map to query.
 * @param {string} key The reference key.
 * @returns {*} Returns the map data.
 */
function getMapData(map, key) {
  var data = map.__data__;
  return isKeyable(key)
    ? data[typeof key == 'string' ? 'string' : 'hash']
    : data.map;
}

/**
 * Gets the property names, values, and compare flags of `object`.
 *
 * @private
 * @param {Object} object The object to query.
 * @returns {Array} Returns the match data of `object`.
 */
//獲取對象中的屬性名，屬性值，和用來匹配的標記
function getMatchData(object) {
  var result = keys(object),//object的key組成的數組
      length = result.length;//key數組的長度

  while (length--) {//循環
    var key = result[length],//當前key
        value = object[key];//當前值

    result[length] = [key, value, isStrictComparable(value)];
    //重寫result的當前值，變成[key, value, boolean]的形式，第三個布爾值代表當前值是否適合用===比較
  }
  return result;
}

/**
 * Gets the native function at `key` of `object`.
 *
 * @private
 * @param {Object} object The object to query.
 * @param {string} key The key of the method to get.
 * @returns {*} Returns the function if it's native, else `undefined`.
 */
function getNative(object, key) {
  var value = getValue(object, key);
  return baseIsNative(value) ? value : undefined;
}

/**
 * Gets the `toStringTag` of `value`.
 *
 * @private
 * @param {*} value The value to query.
 * @returns {string} Returns the `toStringTag`.
 */
var getTag = baseGetTag;

// Fallback for data views, maps, sets, and weak maps in IE 11,
// for data views in Edge < 14, and promises in Node.js.
if ((DataView && getTag(new DataView(new ArrayBuffer(1))) != dataViewTag) ||
    (Map && getTag(new Map) != mapTag) ||
    (Promise && getTag(Promise.resolve()) != promiseTag) ||
    (Set && getTag(new Set) != setTag) ||
    (WeakMap && getTag(new WeakMap) != weakMapTag)) {
  getTag = function(value) {
    var result = objectToString.call(value),
        Ctor = result == objectTag ? value.constructor : undefined,
        ctorString = Ctor ? toSource(Ctor) : undefined;

    if (ctorString) {
      switch (ctorString) {
        case dataViewCtorString: return dataViewTag;
        case mapCtorString: return mapTag;
        case promiseCtorString: return promiseTag;
        case setCtorString: return setTag;
        case weakMapCtorString: return weakMapTag;
      }
    }
    return result;
  };
}

/**
 * Checks if `path` exists on `object`.
 *
 * @private
 * @param {Object} object The object to query.
 * @param {Array|string} path The path to check.
 * @param {Function} hasFunc The function to check properties.
 * @returns {boolean} Returns `true` if `path` exists, else `false`.
 */
//判斷object中是否存在path路徑，考慮深層path路徑
//object給定對象，path給定路徑，hasFunc只判斷一層路徑的基礎方法
function hasPath(object, path, hasFunc) {
  path = isKey(path, object) ? [path] : castPath(path);//將路徑轉換成路徑數組

  var result,//結果布爾值
      index = -1,//循環索引
      length = path.length;//路徑數組的長度

  while (++index < length) {//循環路徑數組
    var key = toKey(path[index]);//轉換key值爲合法key值
    if (!(result = object != null && hasFunc(object, key))) {
      //若是有哪一層不存在，就跳出循環且result賦值false
      break;
    }
    //不然繼續獲取下一層
    object = object[key];
  }
  if (result) {//若是循環結束後result爲true，說明存在此路徑，返回true
    return result;
  }
  var length = object ? object.length : 0;
  return !!length && isLength(length) && isIndex(key, length) &&
    (isArray(object) || isArguments(object));
  //判斷object是數組的狀況
  //有length屬性，length屬性是有效數字，判斷最後一個key值是不是一個數組有效索引，object是數組或者是一個arguments對象
}

/**
 * Checks if `value` is a valid array-like index.
 *
 * @private
 * @param {*} value The value to check.
 * @param {number} [length=MAX_SAFE_INTEGER] The upper bounds of a valid index.
 * @returns {boolean} Returns `true` if `value` is a valid index, else `false`.
 */
//檢查一個值是不是一個有效的array-like的索引
function isIndex(value, length) {
  length = length == null ? MAX_SAFE_INTEGER : length;//若是length是空就換成最大安全數字
  return !!length &&
    (typeof value == 'number' || reIsUint.test(value)) &&
    (value > -1 && value % 1 == 0 && value < length);
    //length存在
    //value是number值或者value符合reIsUint = /^(?:0|[1-9]\d*)$/正則
    //value是正數，value是整數，value小於length
}

/**
 * Checks if `value` is a property name and not a property path.
 *
 * @private
 * @param {*} value The value to check.
 * @param {Object} [object] The object to query keys on.
 * @returns {boolean} Returns `true` if `value` is a property name, else `false`.
 */
function isKey(value, object) {//value用於檢查的值，object用於在其中查詢是否存在value屬性的對象
  if (isArray(value)) {//若是value是數組，返回false，說明value是一個屬性路徑
    return false;
  }
  var type = typeof value;
  if (type == 'number' || type == 'symbol' || type == 'boolean' ||
      value == null || isSymbol(value)) {//若是value是以上類型，則是屬性名，返回true
    return true;
  }
  return reIsPlainProp.test(value) || !reIsDeepProp.test(value) ||
    (object != null && value in Object(object));
    //判斷字符串的狀況，第一個正則reIsPlainProp判斷若是都是單詞說明是屬性名
    //第二個正則reIsDeepProp判斷若是含有點.或者含有數組說明不是屬性名
    //第三種狀況若是value在object裏能找到說明是屬性名
}

/**
 * Checks if `value` is suitable for use as unique object key.
 *
 * @private
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is suitable, else `false`.
 */
function isKeyable(value) {
  var type = typeof value;
  return (type == 'string' || type == 'number' || type == 'symbol' || type == 'boolean')
    ? (value !== '__proto__')
    : (value === null);
}

/**
 * Checks if `func` has its source masked.
 *
 * @private
 * @param {Function} func The function to check.
 * @returns {boolean} Returns `true` if `func` is masked, else `false`.
 */
function isMasked(func) {
  return !!maskSrcKey && (maskSrcKey in func);
}

/**
 * Checks if `value` is likely a prototype object.
 *
 * @private
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is a prototype, else `false`.
 */
function isPrototype(value) {
  var Ctor = value && value.constructor,
      proto = (typeof Ctor == 'function' && Ctor.prototype) || objectProto;

  return value === proto;
}

/**
 * Checks if `value` is suitable for strict equality comparisons, i.e. `===`.
 *
 * @private
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` if suitable for strict
 *  equality comparisons, else `false`.
 */
//檢查一個值用嚴格等於===來比較是否合適
//這個值不是NaN也不是對象就符合要求
function isStrictComparable(value) {
  return value === value && !isObject(value);
}

/**
 * A specialized version of `matchesProperty` for source values suitable
 * for strict equality comparisons, i.e. `===`.
 *
 * @private
 * @param {string} key The key of the property to get.
 * @param {*} srcValue The value to match.
 * @returns {Function} Returns the new spec function.
 */
//返回一個方法，這個方法用於比較傳入對象object key值對應的值是否和給定值srcValue相等
function matchesStrictComparable(key, srcValue) {
  return function(object) {
    if (object == null) {//若是傳入對象爲空，返回false
      return false;
    }
    return object[key] === srcValue &&
      (srcValue !== undefined || (key in Object(object)));
      //給定值不爲undefined且object中有此key值，且key對應值和給定值嚴格嚴格相等，就返回true
  };
}

/**
 * Converts `string` to a property path array.
 *
 * @private
 * @param {string} string The string to convert.
 * @returns {Array} Returns the property path array.
 */
//轉換字符串值變爲屬性path數組
var stringToPath = memoize(function(string) {
  string = toString(string);//將值轉換成字符串

  var result = [];//結果數組
  if (reLeadingDot.test(string)) {
    //reLeadingDot = /^\./，判斷字符串的開頭若是是一個點，結果數組第一個就push一個空字符串
    result.push('');
  }
  string.replace(rePropName, function(match, number, quote, string) {
    //rePropName = /[^.[\]]+|\[(?:(-?\d+(?:\.\d+)?)|(["'])((?:(?!\2)[^\\]|\\.)*?)\2)\]|(?=(?:\.|\[\])(?:\.|\[\]|$))/g;
    //rePropName這個正則匹配三種形式
    //?:是非捕獲分組
    //第一種形式：不是點.也不是[或者]的任意字符組成的字符串，例如：'aaassssdfdffdf'
    //第二種形式：判斷取數組下標的狀況，例如：a[0].b.c.a[0][1]
    //第三種形式：？？？
    result.push(quote ? string.replace(reEscapeChar, '$1') : (number || match));
    //reEscapeChar = /\\(\\)?/g
    //match是匹配到的內容，number是第二種形式的第一個捕獲分組，quote是第二種形式的第二個捕獲分組
    //有quote說明是帶引號的內容，再執行一次replace操做，？？？
  });
  return result;
});

/**
 * Converts `value` to a string key if it's not a string or symbol.
 *
 * @private
 * @param {*} value The value to inspect.
 * @returns {string|symbol} Returns the key.
 */
//若是一個值不是string或者symbol，就把它轉換成string
function toKey(value) {
  if (typeof value == 'string' || isSymbol(value)) {//若是這個值是字符串或者symbol，直接返回
    return value;
  }
  var result = (value + '');//轉換成字符串
  return (result == '0' && (1 / value) == -INFINITY) ? '-0' : result;//判斷value是負0的狀況
}

/**
 * Converts `func` to its source code.
 *
 * @private
 * @param {Function} func The function to process.
 * @returns {string} Returns the source code.
 */
function toSource(func) {
  if (func != null) {
    try {
      return funcToString.call(func);
    } catch (e) {}
    try {
      return (func + '');
    } catch (e) {}
  }
  return '';
}

/**
 * Creates a slice of `array` excluding elements dropped from the end.
 * Elements are dropped until `predicate` returns falsey. The predicate is
 * invoked with three arguments: (value, index, array).
 *
 * @static
 * @memberOf _
 * @since 3.0.0
 * @category Array
 * @param {Array} array The array to query.
 * @param {Function} [predicate=_.identity] The function invoked per iteration.
 * @returns {Array} Returns the slice of `array`.
 * @example
 *
 * var users = [
 *   { 'user': 'barney',  'active': true },
 *   { 'user': 'fred',    'active': false },
 *   { 'user': 'pebbles', 'active': false }
 * ];
 *
 * _.dropRightWhile(users, function(o) { return !o.active; });
 * // => objects for ['barney']
 *
 * // The `_.matches` iteratee shorthand.
 * _.dropRightWhile(users, { 'user': 'pebbles', 'active': false });
 * // => objects for ['barney', 'fred']
 *
 * // The `_.matchesProperty` iteratee shorthand.
 * _.dropRightWhile(users, ['active', false]);
 * // => objects for ['barney']
 *
 * // The `_.property` iteratee shorthand.
 * _.dropRightWhile(users, 'active');
 * // => objects for ['barney', 'fred', 'pebbles']
 */
//建立一個數組的切片，從結尾開始排除掉一些元素，直到根據predicate參數返回false的時候的index就是slice的結束索引
function dropRightWhile(array, predicate) {
  return (array && array.length)
    ? baseWhile(array, baseIteratee(predicate, 3), true, true)
    : [];
    //若是數組不爲空且長度不爲0，就調用baseWhile來處理，不然返回空數組
    //baseWhile第一個參數array爲處理的數組，第二個參數調用baseIteratee生成一個爲判斷須要丟棄的元素的函數，第三個參數isDrop丟棄仍是獲取元素，第四個參數FromRight是否從右往左判斷要丟棄的元素
}

/**
 * Creates a function that memoizes the result of `func`. If `resolver` is
 * provided, it determines the cache key for storing the result based on the
 * arguments provided to the memoized function. By default, the first argument
 * provided to the memoized function is used as the map cache key. The `func`
 * is invoked with the `this` binding of the memoized function.
 *
 * **Note:** The cache is exposed as the `cache` property on the memoized
 * function. Its creation may be customized by replacing the `_.memoize.Cache`
 * constructor with one whose instances implement the
 * [`Map`](http://ecma-international.org/ecma-262/7.0/#sec-properties-of-the-map-prototype-object)
 * method interface of `delete`, `get`, `has`, and `set`.
 *
 * @static
 * @memberOf _
 * @since 0.1.0
 * @category Function
 * @param {Function} func The function to have its output memoized.
 * @param {Function} [resolver] The function to resolve the cache key.
 * @returns {Function} Returns the new memoized function.
 * @example
 *
 * var object = { 'a': 1, 'b': 2 };
 * var other = { 'c': 3, 'd': 4 };
 *
 * var values = _.memoize(_.values);
 * values(object);
 * // => [1, 2]
 *
 * values(other);
 * // => [3, 4]
 *
 * object.a = 2;
 * values(object);
 * // => [1, 2]
 *
 * // Modify the result cache.
 * values.cache.set(object, ['a', 'b']);
 * values(object);
 * // => ['a', 'b']
 *
 * // Replace `_.memoize.Cache`.
 * _.memoize.Cache = WeakMap;
 */
//建立一個能夠緩存func的結果的函數，resolver用來解析緩存result的鍵
function memoize(func, resolver) {
  if (typeof func != 'function' || (resolver && typeof resolver != 'function')) {
    //func和resolver（若是提供的話）若是不是函數，拋錯誤
    throw new TypeError(FUNC_ERROR_TEXT);
  }
  var memoized = function() {
    var args = arguments,
        key = resolver ? resolver.apply(this, args) : args[0],
        //若是提供了resolver，就用resolver來肯定key，不然key就是memoized的第一個參數
        cache = memoized.cache;//cashe對象

    if (cache.has(key)) {//若是cache中已經有此key，就直接獲取後返回
      return cache.get(key);
    }
    var result = func.apply(this, args);//不然調用func計算出key對應的value
    memoized.cache = cache.set(key, result);//將新value存入cache後返回
    return result;
  };
  memoized.cache = new (memoize.Cache || MapCache);//cache使用自定義的MapCache類型
  return memoized;
}

// Assign cache to `_.memoize`.
memoize.Cache = MapCache;

/**
 * Performs a
 * [`SameValueZero`](http://ecma-international.org/ecma-262/7.0/#sec-samevaluezero)
 * comparison between two values to determine if they are equivalent.
 *
 * @static
 * @memberOf _
 * @since 4.0.0
 * @category Lang
 * @param {*} value The value to compare.
 * @param {*} other The other value to compare.
 * @returns {boolean} Returns `true` if the values are equivalent, else `false`.
 * @example
 *
 * var object = { 'a': 1 };
 * var other = { 'a': 1 };
 *
 * _.eq(object, object);
 * // => true
 *
 * _.eq(object, other);
 * // => false
 *
 * _.eq('a', 'a');
 * // => true
 *
 * _.eq('a', Object('a'));
 * // => false
 *
 * _.eq(NaN, NaN);
 * // => true
 */
//判斷兩個值是否相等
function eq(value, other) {
  return value === other || (value !== value && other !== other);
}

/**
 * Checks if `value` is likely an `arguments` object.
 *
 * @static
 * @memberOf _
 * @since 0.1.0
 * @category Lang
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is an `arguments` object,
 *  else `false`.
 * @example
 *
 * _.isArguments(function() { return arguments; }());
 * // => true
 *
 * _.isArguments([1, 2, 3]);
 * // => false
 */
//判斷一個值是一個相似arguments對象 
function isArguments(value) {
  // Safari 8.1 makes `arguments.callee` enumerable in strict mode.
  return isArrayLikeObject(value) && hasOwnProperty.call(value, 'callee') &&
    (!propertyIsEnumerable.call(value, 'callee') || objectToString.call(value) == argsTag);
    //value是一個array-like對象，value有名爲callee的自身屬性，callee屬性不可枚舉，對象的toString標籤是'[object Arguments]'
}

/**
 * Checks if `value` is classified as an `Array` object.
 *
 * @static
 * @memberOf _
 * @since 0.1.0
 * @category Lang
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is an array, else `false`.
 * @example
 *
 * _.isArray([1, 2, 3]);
 * // => true
 *
 * _.isArray(document.body.children);
 * // => false
 *
 * _.isArray('abc');
 * // => false
 *
 * _.isArray(_.noop);
 * // => false
 */
//判斷一個值是否是數組對象
var isArray = Array.isArray;

/**
 * Checks if `value` is array-like. A value is considered array-like if it's
 * not a function and has a `value.length` that's an integer greater than or
 * equal to `0` and less than or equal to `Number.MAX_SAFE_INTEGER`.
 *
 * @static
 * @memberOf _
 * @since 4.0.0
 * @category Lang
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is array-like, else `false`.
 * @example
 *
 * _.isArrayLike([1, 2, 3]);
 * // => true
 *
 * _.isArrayLike(document.body.children);
 * // => true
 *
 * _.isArrayLike('abc');
 * // => true
 *
 * _.isArrayLike(_.noop);
 * // => false
 */
//判斷一個值是不是一個array-like
//規則：不等於null，不是function類型，而且有length屬性，length是大於0小於Number.MAX_SAFE_INTEGER的整數
function isArrayLike(value) {
  return value != null && isLength(value.length) && !isFunction(value);
}

/**
 * This method is like `_.isArrayLike` except that it also checks if `value`
 * is an object.
 *
 * @static
 * @memberOf _
 * @since 4.0.0
 * @category Lang
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is an array-like object,
 *  else `false`.
 * @example
 *
 * _.isArrayLikeObject([1, 2, 3]);
 * // => true
 *
 * _.isArrayLikeObject(document.body.children);
 * // => true
 *
 * _.isArrayLikeObject('abc');
 * // => false
 *
 * _.isArrayLikeObject(_.noop);
 * // => false
 */
//判斷一個值是否是一個array-like對象
//isObjectLike判斷一個值是不是一個object-like，規則是：typeof返回object，而且不是null
//isArrayLike判斷一個值是不是一個array-like，規則：不等於null，不是function類型，而且有length屬性，length是大於0小於Number.MAX_SAFE_INTEGER的整數
function isArrayLikeObject(value) {
  return isObjectLike(value) && isArrayLike(value);
}

/**
 * Checks if `value` is classified as a `Function` object.
 *
 * @static
 * @memberOf _
 * @since 0.1.0
 * @category Lang
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is a function, else `false`.
 * @example
 *
 * _.isFunction(_);
 * // => true
 *
 * _.isFunction(/abc/);
 * // => false
 */
//判斷一個值是不是Function對象
function isFunction(value) {
  // The use of `Object#toString` avoids issues with the `typeof` operator
  // in Safari 8-9 which returns 'object' for typed array and other constructors.
  var tag = isObject(value) ? objectToString.call(value) : '';
  //獲取value的toString tag
  return tag == funcTag || tag == genTag;
  //若是toString tag等於[object Function]，或者[object GeneratorFunction]，說明是function
}

/**
 * Checks if `value` is a valid array-like length.
 *
 * **Note:** This method is loosely based on
 * [`ToLength`](http://ecma-international.org/ecma-262/7.0/#sec-tolength).
 *
 * @static
 * @memberOf _
 * @since 4.0.0
 * @category Lang
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is a valid length, else `false`.
 * @example
 *
 * _.isLength(3);
 * // => true
 *
 * _.isLength(Number.MIN_VALUE);
 * // => false
 *
 * _.isLength(Infinity);
 * // => false
 *
 * _.isLength('3');
 * // => false
 */
//判斷一個值是不是一個有效的array-like對象的length屬性
function isLength(value) {
  return typeof value == 'number' &&
    value > -1 && value % 1 == 0 && value <= MAX_SAFE_INTEGER;
    //是number類型，是正數，是整數不是小數，在最大數字範圍內
}

/**
 * Checks if `value` is the
 * [language type](http://www.ecma-international.org/ecma-262/7.0/#sec-ecmascript-language-types)
 * of `Object`. (e.g. arrays, functions, objects, regexes, `new Number(0)`, and `new String('')`)
 *
 * @static
 * @memberOf _
 * @since 0.1.0
 * @category Lang
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is an object, else `false`.
 * @example
 *
 * _.isObject({});
 * // => true
 *
 * _.isObject([1, 2, 3]);
 * // => true
 *
 * _.isObject(_.noop);
 * // => true
 *
 * _.isObject(null);
 * // => false
 */
//判斷一個值是不是一個對象
function isObject(value) {
  var type = typeof value;
  return !!value && (type == 'object' || type == 'function');
}

/**
 * Checks if `value` is object-like. A value is object-like if it's not `null`
 * and has a `typeof` result of "object".
 *
 * @static
 * @memberOf _
 * @since 4.0.0
 * @category Lang
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is object-like, else `false`.
 * @example
 *
 * _.isObjectLike({});
 * // => true
 *
 * _.isObjectLike([1, 2, 3]);
 * // => true
 *
 * _.isObjectLike(_.noop);
 * // => false
 *
 * _.isObjectLike(null);
 * // => false
 */
//判斷一個值是不是一個object-like，規則是：typeof返回object，而且不是null
function isObjectLike(value) {
  return !!value && typeof value == 'object';
}

/**
 * Checks if `value` is classified as a `Symbol` primitive or object.
 *
 * @static
 * @memberOf _
 * @since 4.0.0
 * @category Lang
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is a symbol, else `false`.
 * @example
 *
 * _.isSymbol(Symbol.iterator);
 * // => true
 *
 * _.isSymbol('abc');
 * // => false
 */
//判斷一個值是不是原生的Symbol對象
function isSymbol(value) {
  return typeof value == 'symbol' ||
    (isObjectLike(value) && objectToString.call(value) == symbolTag);
}

/**
 * Checks if `value` is classified as a typed array.
 *
 * @static
 * @memberOf _
 * @since 3.0.0
 * @category Lang
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is a typed array, else `false`.
 * @example
 *
 * _.isTypedArray(new Uint8Array);
 * // => true
 *
 * _.isTypedArray([]);
 * // => false
 */
//判斷一個值是typedArray類型，若是是nodejs環境就使用nodejs自帶的優化方法
var isTypedArray = nodeIsTypedArray ? baseUnary(nodeIsTypedArray) : baseIsTypedArray;

/**
 * Converts `value` to a string. An empty string is returned for `null`
 * and `undefined` values. The sign of `-0` is preserved.
 *
 * @static
 * @memberOf _
 * @since 4.0.0
 * @category Lang
 * @param {*} value The value to process.
 * @returns {string} Returns the string.
 * @example
 *
 * _.toString(null);
 * // => ''
 *
 * _.toString(-0);
 * // => '-0'
 *
 * _.toString([1, 2, 3]);
 * // => '1,2,3'
 */
//將一個值轉換成字符串值，空值會返回空字符串
function toString(value) {
  return value == null ? '' : baseToString(value);
}

/**
 * Gets the value at `path` of `object`. If the resolved value is
 * `undefined`, the `defaultValue` is returned in its place.
 *
 * @static
 * @memberOf _
 * @since 3.7.0
 * @category Object
 * @param {Object} object The object to query.
 * @param {Array|string} path The path of the property to get.
 * @param {*} [defaultValue] The value returned for `undefined` resolved values.
 * @returns {*} Returns the resolved value.
 * @example
 *
 * var object = { 'a': [{ 'b': { 'c': 3 } }] };
 *
 * _.get(object, 'a[0].b.c');
 * // => 3
 *
 * _.get(object, ['a', '0', 'b', 'c']);
 * // => 3
 *
 * _.get(object, 'a.b.c', 'default');
 * // => 'default'
 */
//根據path來獲取object上對應健的值
function get(object, path, defaultValue) {
  var result = object == null ? undefined : baseGet(object, path);//根據路徑獲取值
  return result === undefined ? defaultValue : result;//若是結果是undefined，返回默認值
}

/**
 * Checks if `path` is a direct or inherited property of `object`.
 *
 * @static
 * @memberOf _
 * @since 4.0.0
 * @category Object
 * @param {Object} object The object to query.
 * @param {Array|string} path The path to check.
 * @returns {boolean} Returns `true` if `path` exists, else `false`.
 * @example
 *
 * var object = _.create({ 'a': _.create({ 'b': 2 }) });
 *
 * _.hasIn(object, 'a');
 * // => true
 *
 * _.hasIn(object, 'a.b');
 * // => true
 *
 * _.hasIn(object, ['a', 'b']);
 * // => true
 *
 * _.hasIn(object, 'b');
 * // => false
 */
//判斷path路徑在給定object中是否存在
function hasIn(object, path) {
  return object != null && hasPath(object, path, baseHasIn);
}

/**
 * Creates an array of the own enumerable property names of `object`.
 *
 * **Note:** Non-object values are coerced to objects. See the
 * [ES spec](http://ecma-international.org/ecma-262/7.0/#sec-object.keys)
 * for more details.
 *
 * @static
 * @since 0.1.0
 * @memberOf _
 * @category Object
 * @param {Object} object The object to query.
 * @returns {Array} Returns the array of property names.
 * @example
 *
 * function Foo() {
 *   this.a = 1;
 *   this.b = 2;
 * }
 *
 * Foo.prototype.c = 3;
 *
 * _.keys(new Foo);
 * // => ['a', 'b'] (iteration order is not guaranteed)
 *
 * _.keys('hi');
 * // => ['0', '1']
 */
//將對象可枚舉的屬性的key提取出來建立一個新數組，與Object.keys同樣的效果
function keys(object) {
  return isArrayLike(object) ? arrayLikeKeys(object) : baseKeys(object);
  //先判斷object是不是array-like對象，若是是調用arrayLikeKeys，若是不是調用baseKeys
}

/**
 * This method returns the first argument it receives.
 *
 * @static
 * @since 0.1.0
 * @memberOf _
 * @category Util
 * @param {*} value Any value.
 * @returns {*} Returns `value`.
 * @example
 *
 * var object = { 'a': 1 };
 *
 * console.log(_.identity(object) === object);
 * // => true
 */
//用做默認迭代器，直接返回接收到的第一個參數
function identity(value) {
  return value;
}

/**
 * Creates a function that returns the value at `path` of a given object.
 *
 * @static
 * @memberOf _
 * @since 2.4.0
 * @category Util
 * @param {Array|string} path The path of the property to get.
 * @returns {Function} Returns the new accessor function.
 * @example
 *
 * var objects = [
 *   { 'a': { 'b': 2 } },
 *   { 'a': { 'b': 1 } }
 * ];
 *
 * _.map(objects, _.property('a.b'));
 * // => [2, 1]
 *
 * _.map(_.sortBy(objects, _.property(['a', 'b'])), 'a.b');
 * // => [1, 2]
 */
//建立一個方法，這個方法能夠根據給定path屬性路徑返回給定對象的屬性值
function property(path) {
  return isKey(path) ? baseProperty(toKey(path)) : basePropertyDeep(path);
  //先判斷path是key仍是path
  //若是是key，調用baseProperty，返回一個方法，這個方法返回object的對應key的對應value
  //若是是路徑，調用basePropertyDeep，返回一個方法，這個方法根據path返回object的對應屬性值
}

module.exports = dropRightWhile;