--- /dev/null
+var isArray = require('./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)));
+}
+
+module.exports = isKey;