@talkol Hi
What is get method to get state?
Or where can I find info?

Since there is an add method, is there "substract" method?

sub?

GitHub - indutny/bn.js: BigNum in pure javascript
https://github.com/indutny/bn.js#arithmetics

I believe TonWeb is the most up to date. It's not feature complete, but it should have the most common things.

There’s a function called getChannelState that you can call: https://github.com/toncenter/tonweb/blob/master/src/contract/payments/PaymentChannel.js#L331

You can see the rest of the methods in this source file