Apply suggestions from code review

Co-authored-by: Uzlopak <[email protected]>

Author: Eomm

standalone.js

@@ -3,11 +3,11 @@
 const SerializerSelector = require('./index')
 
 function StandaloneSerializer (options = { readMode: true }) {
-  if (options.readMode === true && !options.restoreFunction) {
+  if (options.readMode === true && typeof options.restoreFunction !== 'function') {
     throw new Error('You must provide a restoreFunction options when readMode ON')
   }
 
-  if (options.readMode !== true && !options.storeFunction) {
+  if (options.readMode !== true && typeof options.storeFunction !== 'function') {
     throw new Error('You must provide a storeFunction options when readMode OFF')
   }