code review improvement

Author: slax57

src/introspection/DateType.js

@@ -1,9 +1,11 @@
 import { GraphQLScalarType, GraphQLError } from 'graphql';
 import { Kind } from 'graphql/language';
 
+const ISO_DATE_STRING_PATTERN = /\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}.\d{3}Z/;
+
 export const isISODateString = (value) => {
     if (typeof value !== 'string') return false;
-    if (!/\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}.\d{3}Z/.test(value)) return false;
+    if (!ISO_DATE_STRING_PATTERN.test(value)) return false;
     const d = new Date(value);
     return d.toISOString() === value;
 };