Bump to v4.1.0.

_isKey.js

@@ -0,0 +1,25 @@
+define(['./isArray'], function(isArray) {
+
+  /** Used to match property names within property paths. */
+  var reIsDeepProp = /\.|\[(?:[^[\]]*|(["'])(?:(?!\1)[^\\]|\\.)*?\1)\]/,
+      reIsPlainProp = /^\w*$/;
+
+  /**
+   * 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) {
+    if (typeof value == 'number') {
+      return true;
+    }
+    return !isArray(value) &&
+      (reIsPlainProp.test(value) || !reIsDeepProp.test(value) ||
+        (object != null && value in Object(object)));
+  }
+
+  return isKey;
+});