Bump to v4.1.0.

_indexKeys.js

@@ -0,0 +1,24 @@
+import baseTimes from './_baseTimes';
+import isArguments from './isArguments';
+import isArray from './isArray';
+import isLength from './isLength';
+import isString from './isString';
+
+/**
+ * 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|null} Returns index keys, else `null`.
+ */
+function indexKeys(object) {
+  var length = object ? object.length : undefined;
+  if (isLength(length) &&
+      (isArray(object) || isString(object) || isArguments(object))) {
+    return baseTimes(length, String);
+  }
+  return null;
+}
+
+export default indexKeys;