Bcoin is thoroughly event driven. It has a fullnode object, but Bcoin was specifically designed so the mempool, blockchain, p2p pool, and wallet database could all be used separately. All the fullnode object does is tie these things together. It's essentially a huge proxying of events. The general communication between these things looks something like this:
pool -> block event -> chain
pool -> tx event -> mempool
chain -> block event -> mempool/miner
chain -> tx event -> walletdb
chain -> reorg event -> walletdb/mempool/miner
mempool -> tx event -> walletdb/miner
miner -> block event -> chain
walletdb -> tx event -> websocket server
websocket server -> tx event -> websocket client
http client -> tx -> http server -> mempool
Not only does the loose coupling make testing easier, it ensures people can utilize bcoin for many use cases.
Non-javscript people reading this may think using javascript isn't a wise decision.
Javascript is inherently slow due to how dynamic it is, but modern JITs have solved this issue using very clever optimization and dynamic recompilation techniques. v8 in some cases can rival the speed of C++ if the code is well-written.
Bcoin runs in node.js, so the javascript code is limited to one thread. We solve this limitation by spinning up persistent worker processes for transaction verification (webworkers when in the browser). This ensures the blockchain and mempool do not block the master process very much. It also means transaction verification can be parallelized.
Strangely enough, workers are faster in the browser than they are in node since you are allowed to share memory between threads using the transferrable api (Uint8Arrays can be "transferred" to another thread). In node, you have to pipe data to another process.
But of course, there is a benefit to having a multi-process architecture: the worker processes can die on their own without disturbing the master process.
Bcoin uses secp256k1-node for ecdsa verification, which is a node.js binding to Pieter Wuille's blazingly fast libsecp256k1 library.
In the browser, bcoin will use elliptic, the fastest javascript ecdsa implementation. It will obviously never beat C and hand-optimized assembly, but it's still usable.
The real feature of javascript is that your code will run almost anywhere. With bcoin, we now have a full node that will run on almost any browser, on laptops, on servers, on smartphones, on most devices you can imagine, even by simply visiting a webpage.