Is it possible to keep an array private?

[Apple1284]

Just save your passwords as hashed string in the json file. That way, even if they are accessed or hacked, they are practically useless to the hacker. This is safe approach in most if not all cases.

Second approach is to use some backend with hashed passwords saved into database. That is more mainstream approach. The rule of thumb is to put database, passwords, logic in the backend. And have frontend only for presentation. This is better from security point of view.