Ensure _.keys and _.keysIn skip "length" keys for strict mode arguments objects in Safari 9.

lodash.js

@@ -4764,20 +4764,18 @@
     }
 
     /**
-     * Initializes an array of property names based on `object`. If `object` is
-     * an array, `arguments` object, or `string` its index keys are returned,
-     * otherwise an empty array is returned.
+     * Creates an array of index keys for `object` values of arrays,
+     * `arguments` objects, and strings, otherwise `null` is returned.
      *
      * @private
      * @param {Object} object The object to query.
-     * @returns {Array} Returns the initialized array of property names.
+     * @returns {Array|null} Returns index keys, else `null`.
      */
-    function initKeys(object) {
-      var length = object ? object.length : 0;
-      length = (length && isLength(length) &&
-        (isArray(object) || isString(object) || isArguments(object)) && length) || 0;
-
-      return baseTimes(length, String);
+    function indexKeys(object) {
+      var length = object ? object.length : undefined;
+      return (isLength(length) && (isArray(object) || isString(object) || isArguments(object)))
+        ? baseTimes(length, String)
+        : null;
     }
 
     /**
@@ -10808,13 +10806,14 @@
       if (!(isProto || isArrayLike(object))) {
         return baseKeys(object);
       }
-      var result = initKeys(object),
-          length = result.length,
-          skipIndexes = !!length;
+      var indexes = indexKeys(object),
+          skipIndexes = !!indexes,
+          result = indexes || [],
+          length = result.length;
 
       for (var key in object) {
         if (baseHas(object, key) &&
-            !(skipIndexes && isIndex(key, length)) &&
+            !(skipIndexes && (key == 'length' || isIndex(key, length))) &&
             !(isProto && key == 'constructor')) {
           result.push(key);
         }
@@ -10849,13 +10848,14 @@
           isProto = isPrototype(object),
           props = baseKeysIn(object),
           propsLength = props.length,
-          result = initKeys(object),
-          length = result.length,
-          skipIndexes = !!length;
+          indexes = indexKeys(object),
+          skipIndexes = !!indexes,
+          result = indexes || [],
+          length = result.length;
 
       while (++index < propsLength) {
         var key = props[index];
-        if (!(skipIndexes && isIndex(key, length)) &&
+        if (!(skipIndexes && (key == 'length' || isIndex(key, length))) &&
             !(key == 'constructor' && (isProto || !hasOwnProperty.call(object, key)))) {
           result.push(key);
         }

test/test.js

@@ -10678,7 +10678,8 @@
   QUnit.module('keys methods');
 
   lodashStable.each(['keys', 'keysIn'], function(methodName) {
-    var args = arguments,
+    var args = (function() { return arguments; }(1, 2, 3)),
+        strictArgs = (function() { 'use strict'; return arguments; }(1, 2, 3)),
         func = _[methodName],
         isKeys = methodName == 'keys';
 
@@ -10740,25 +10741,43 @@
     QUnit.test('`_.' + methodName + '` should work with `arguments` objects', function(assert) {
       assert.expect(1);
 
-      assert.deepEqual(func(args).sort(), ['0', '1', '2']);
+      var values = [args, strictArgs],
+          expected = lodashStable.map(values, lodashStable.constant(['0', '1', '2'])),
+          actual = lodashStable.map(values, func);
+
+      assert.deepEqual(actual, expected);
     });
 
     QUnit.test('`_.' + methodName + '` should return keys for custom properties on `arguments` objects', function(assert) {
       assert.expect(1);
 
-      args.a = 1;
-      assert.deepEqual(func(args).sort(), ['0', '1', '2', 'a']);
-      delete args.a;
+      var values = [args, strictArgs],
+          expected = lodashStable.map(values, lodashStable.constant(['0', '1', '2', 'a']));
+
+      var actual = lodashStable.map(values, function(value) {
+        value.a = 1;
+        var result = func(value).sort();
+        delete value.a;
+        return result;
+      });
+
+      assert.deepEqual(actual, expected);
     });
 
     QUnit.test('`_.' + methodName + '` should ' + (isKeys ? 'not' : '') + ' include inherited properties of `arguments` objects', function(assert) {
       assert.expect(1);
 
-      var expected = isKeys ? ['0', '1', '2'] : ['0', '1', '2', 'a'];
+      var values = [args, strictArgs],
+          expected = lodashStable.map(values, lodashStable.constant(isKeys ? ['0', '1', '2'] : ['0', '1', '2', 'a']));
 
-      objectProto.a = 1;
-      assert.deepEqual(func(args).sort(), expected);
-      delete objectProto.a;
+      var actual = lodashStable.map(values, function(value) {
+        objectProto.a = 1;
+        var result = func(value).sort();
+        delete objectProto.a;
+        return result;
+      });
+
+      assert.deepEqual(actual, expected);
     });
 
     QUnit.test('`_.' + methodName + '` should work with string objects', function(assert) {