add book.js

node_modules/lodash/internal/mapGet.js

@@ -0,0 +1,14 @@
+/**
+ * Gets the cached value for `key`.
+ *
+ * @private
+ * @name get
+ * @memberOf _.memoize.Cache
+ * @param {string} key The key of the value to get.
+ * @returns {*} Returns the cached value.
+ */
+function mapGet(key) {
+  return key == '__proto__' ? undefined : this.__data__[key];
+}
+
+module.exports = mapGet;