add book.js

node_modules/lodash/internal/mergeDefaults.js

@@ -0,0 +1,15 @@
+var merge = require('../object/merge');
+
+/**
+ * Used by `_.defaultsDeep` to customize its `_.merge` use.
+ *
+ * @private
+ * @param {*} objectValue The destination object property value.
+ * @param {*} sourceValue The source object property value.
+ * @returns {*} Returns the value to assign to the destination object.
+ */
+function mergeDefaults(objectValue, sourceValue) {
+  return objectValue === undefined ? sourceValue : merge(objectValue, sourceValue, mergeDefaults);
+}
+
+module.exports = mergeDefaults;