> It was never slow. The event loop is very performant compared to a language with a GIL and a culture of synchronous IO (looking at you, python and ruby), and

> It was never slow. The event loop is very performant compared to a language with a GIL and a culture of synchronous IO (looking at you, python and ruby), and V8 is amazing. Having written a lot of code in both Python and JavaScript I disagree here. It's not really the GIL slows down Python compared to JavaScript, that's more down to the lack of a comparable JIT. Yes there's PyPy but it has received a fraction of the investment of V8 and Python is a more complex language to create a good JIT for. Support for multithreading (albeit without parallelism) may be one of a number of factors those complicating factors. JavaScript doesn't need a GIL because it doesn't support multithreading. WebWorkers are more akin to Python's multiprocessing since objects are not shared between threads. You have to be careful doing anything compute intensive (e.g. JSON.parse of a large blob of JSON) when using cooperative (async) rather than preemptive (threads) concurrency since you may inadvertently block the event loop, substantially increasing latency for other tasks. Handing off such tasks to a thread pool is harder in JS than Python since you can't easily deferToThread as you can in an async Python program. Cooperative multitasking has its advantages too of course. An event loop provides a clear boundary for efficiently batching calls which can be awkward with synchronous code. Folks have been writing network servers and in Python using asynchronous techniques for decades now. Twisted is almost 20 years at this point and asyncore was added to the standard library even earlier.