limit query words to list

src/words.ts

@@ -1,14 +1,18 @@
+const defaultMessage = ' Using word of the day instead.'
+
 export function getWordOfTheDay() {
   if (location.search) {
     try {
       const query = atob(location.search.slice(1))
       if (query.length !== 5) {
-      alert('incorrect word length from encoded query.')
+        alert(`Incorrect word length from encoded query. ${defaultMessage}`)
+      } else if (!allWords.includes(query)) {
+        alert(`Encoded query is not in the word list. ${defaultMessage}`)
       } else {
         return query
       }
     } catch (e) {
-      alert('malformed encoded word query.')
+      alert(`Malformed encoded word query. ${defaultMessage}`)
     }
   }