Add initCloneByTag and adjust how unclonables are handled.

lodash.compat.js

@@ -1815,21 +1815,35 @@
       if (typeof result != 'undefined') {
         return result;
       }
-      var isArr = isArray(value);
-      result = value;
-      if (isArr) {
-        result = initArrayClone(value, isDeep);
-      } else if (isObject(value)) {
-        result = initObjectClone(value, isDeep);
-        if (result === null) {
-          isDeep = false;
-          result = {};
-        } else if (isDeep) {
-          isDeep = objToString.call(result) == objectTag;
-        }
+      if (!isObject(value)) {
+        return value;
       }
-      if (!isDeep || result === value) {
-        return result;
+      var isArr = isArray(value);
+      if (isArr) {
+        result = initCloneArray(value);
+        if (!isDeep) {
+          return arrayCopy(value, result);
+        }
+      } else {
+        var tag = objToString.call(value),
+            isFunc = tag == funcTag;
+
+        if (!lodash.support.argsTag && isArguments(value)) {
+          tag = argsTag;
+        }
+        if (tag == objectTag || (isFunc && !object)) {
+          if (isHostObject(value)) {
+            return object ? value : {};
+          }
+          result = initCloneObject(isFunc ? {} : value);
+          if (!isDeep) {
+            return baseAssign(result, value);
+          }
+        } else {
+          return cloneableTags[tag]
+            ? initCloneByTag(value, tag, isDeep)
+            : (object ? value : {});
+        }
       }
       // Check for circular references and return corresponding clone.
       stackA || (stackA = []);
@@ -3589,22 +3603,16 @@
      *
      * @private
      * @param {Array} array The array to clone.
-     * @param {boolean} [isDeep] Specify a deep clone.
-     * @returns {Array} Returns the initialized array clone.
+     * @returns {Array} Returns the initialized clone.
      */
-    function initArrayClone(array, isDeep) {
+    function initCloneArray(array) {
       var length = array.length,
           result = new array.constructor(length);
 
-      if (length) {
-        if (!isDeep) {
-          arrayCopy(array, result);
-        }
-        // Add array properties assigned by `RegExp#exec`.
-        if (typeof array[0] == 'string' && hasOwnProperty.call(array, 'index')) {
-          result.index = array.index;
-          result.input = array.input;
-        }
+      // Add array properties assigned by `RegExp#exec`.
+      if (length && typeof array[0] == 'string' && hasOwnProperty.call(array, 'index')) {
+        result.index = array.index;
+        result.input = array.input;
       }
       return result;
     }
@@ -3614,30 +3622,37 @@
      *
      * @private
      * @param {Object} object The object to clone.
-     * @param {boolean} [isDeep] Specify a deep clone.
-     * @returns {null|Object} Returns the initialized object clone if an object
-     *  is cloneable, else `null`.
+     * @returns {Object} Returns the initialized clone.
      */
-    function initObjectClone(object, isDeep) {
-      if (!isCloneable(object)) {
-        return null;
-      }
-      var Ctor = object.constructor,
-          tag = objToString.call(object),
-          isArgs = tag == argsTag || (!lodash.support.argsTag && isArguments(object)),
-          isObj = tag == objectTag;
-
-      if (isObj && !(typeof Ctor == 'function' && Ctor instanceof Ctor)) {
+    function initCloneObject(object) {
+      var Ctor = object.constructor;
+      if (!(typeof Ctor == 'function' && Ctor instanceof Ctor)) {
         Ctor = Object;
       }
-      if (isArgs || isObj) {
-        var result = isDeep ? new Ctor : baseAssign(new Ctor, object);
-        if (isArgs) {
-          result.length = object.length;
-        }
-        return result;
-      }
+      return new Ctor;
+    }
+
+    /**
+     * Initializes an object clone based on its `toStringTag`.
+     *
+     * **Note:** This function only supports cloning values with `toStringTag`
+     * values of `Boolean`, `Date`, `Error`, `Number`, `RegExp`, or `String`.
+     *
+     *
+     * @private
+     * @param {Object} object The object to clone.
+     * @param {string} tag The `toStringTag` of the object to clone.
+     * @param {boolean} [isDeep] Specify a deep clone.
+     * @returns {Object} Returns the initialized clone.
+     */
+    function initCloneByTag(object, tag, isDeep) {
+      var Ctor = object.constructor;
       switch (tag) {
+        case argsTag:
+          var result = new Ctor;
+          result.length = object.length;
+          return arrayCopy(object, result);
+
         case arrayBufferTag:
           return bufferClone(object);
 

test/test.js

@@ -1670,6 +1670,7 @@
   (function() {
     function Klass() { this.a = 1; }
     Klass.prototype = { 'b': 1 };
+    Klass.foo = function() {};
 
     var objects = {
       '`arguments` objects': arguments,
@@ -1692,13 +1693,13 @@
 
     objects['arrays'].length = 3;
 
-    var nonCloneable = {
+    var uncloneable = {
       'DOM elements': body,
       'functions': Klass
     };
 
     _.each(errors, function(error) {
-      nonCloneable[error.name + 's'] = error;
+      uncloneable[error.name + 's'] = error;
     });
 
     test('`_.clone` should perform a shallow clone', 2, function() {
@@ -1747,18 +1748,16 @@
         });
       });
 
-      _.forOwn(nonCloneable, function(value, key) {
-        test('`_.' + methodName + '` should not clone ' + key, 2, function() {
+      _.forOwn(uncloneable, function(value, key) {
+        test('`_.' + methodName + '` should not clone ' + key, 3, function() {
           var object = { 'a': value, 'b': { 'c': value } },
-              expected = value && {};
+              actual = func(object);
 
+          notStrictEqual(actual, object);
+          deepEqual(actual, object);
+
+          var expected = typeof value == 'function' ? { 'foo': Klass.foo } : {};
           deepEqual(func(value), expected);
-
-          expected = isDeep
-            ? { 'a': expected, 'b': { 'c': expected } }
-            : { 'a': value,    'b': { 'c': value } }
-
-          deepEqual(func(object), expected);
         });
 
         test('`_.' + methodName + '` should work with a `customizer` callback and ' + key, 4, function() {