You can implement them in javascript or any other language you choose. (Doing so in client side js is probably a stupid idea, but so is pretty much everything in the article. Its definitely possible though)
You have funcs to make public/private key pairs. Funcs to sign things. You can make your own PKI in the usual manner. You could then pin on specific keys in your chain of signatures if you want.
Why you would, i dont know. Its a terrible idea like most use cases for js client side crypto, but you could if you wanted to. Then again, cert pinning is a mostly terrible idea in the context of TLS too.
You can implement them in javascript or any other language you choose. (Doing so in client side js is probably a stupid idea, but so is pretty much everything in the article. Its definitely possible though)