[I_am_tiberius]

My opinion is that websites/provider that handle with the customer's sensitive data should release the source, at least the client side source. I just want to be sure that my data is encrypted on the client side and not accessible by the service provider.

It does not mean everyone should be able to use the code. There are still licenses associated with the published source which can/should prevent others to use the code.

[akjainaj]

The client side source is downloaded and executed by your browser and you can inspect it at any time.

[I_am_tiberius]

Yes, if you use the website. If you use mobile apps that is more difficult.