use array destructuring approach

store/postwoman.js

@@ -51,8 +51,7 @@ export const mutations = {
         if(setting == null || !(setting instanceof Array) || setting.length !== 2)
             throw new Error("You must provide a setting (array in the form [key, value])");
 
-        let key = setting[0];
-        let value = setting[1];
+        const [key, value] = setting;
         // Do not just remove this check.
         // Add your settings key to the SETTINGS_KEYS array at the
         // top of the file.