I just published my new widget BlockChainLedger on WidgetWonk. This widget is a toy for playing with a Merkle chain, which is the technology that blockchains are based on. Each record in the chain is hashed and each record is stored with the hash of the previous record. I rolled my own version of this in JavaScript except for the hashing. For hashing I used a function from the SJCL library.
I used the React framework for this with Redux for state management. Source code is available at https://github.com/xerocross/blockchain-ledger . It includes ample unit testing.
adamcross.blog 