Shameless plug: https://github.com/cryptocoinjs (Bitcoin JavaScript fork of the original BitcoinJS) Right now, we're focused on Bitcoin, but we're moving fast and will be expanding support for altcoins. Also, if you're interested in the intricacies of addresses and Bitcoin, I'd encourage to read a very detailed article that I wrote on Bitcoin Addresses and JavaScript: http://procbits.com/2013/08/27/generating-a-bitcoin-address-... Doesn't use CryptoCoinJS yet as the article was written before I started CryptoCoinJS.