It's relatively straightforward (but moderately involved) to split out CPU-heavy operations in node.js so they don't block the event loop. A rough sketch would look like this:

* Write the CPU-heavy code in C++ and bridge it back to node.js as an add-on: http://nodejs.org/api/addons.html

* node.js is built atop libuv, so use libuv's work queues to offload the CPU-heavy code to a worker thread: http://nikhilm.github.io/uvbook/threads.html