What I think you're missing is that in JS, this is not being run concurrently. Existing JS runtimes are single-threaded—if you actually want to take advantage o

What I think you're missing is that in JS, this is not being run concurrently. Existing JS runtimes are single-threaded—if you actually want to take advantage of multiple CPUs you must run more than one process. It's very easy not to have concurrency bugs when there's no concurrency. In Java, you have access to real threads and can actually run two pieces of code concurrently. This introduces a lot of potential issues, but also allows you to take advantage of multiple cores. If all you want is non-blocking IO (what node gives you), there are a handful of great libraries that provide that on the JVM.