The big strength and at the same time big weakness of nodejs is the asynchronous event loop. If we ignore the cluster setup to get parallelism, concurrency in

The big strength and at the same time big weakness of nodejs is the asynchronous event loop. If we ignore the cluster setup to get parallelism, concurrency in nodejs is done by running all request in the same thread by segmenting them and each sub part of a request into asynchronous callbacks. By doing like this nodejs can achieve high performance because it avoids high cost of thread context switching. The drawback is that one request can block all other request if some code is badly written, if only one callback takes too much time everyone needs to wait until it is finished, remember only one thread, no parallelism. If you compare to PHP where the web server handles all process management (threads or processes), one badly implemented endpoint will most likely not affect other request to other endpoints. (Of course we have same limitations as always being on the same machine, limits on memory, cpu etc). Other endpoints will continue to work as before even if your team committed a few lines of shitty code whereas in nodejs it can bring down the entire system. Avoiding this blocking effect in nodejs is usually not a problem if you are a skilled developer, however if not it is highly likely that you will deploy this behavior to production. That is also in a sense a paradox of nodejs, it is pitched as something easy to pickup if you already know JavaScript, it is true that it is similar to browser JS, which is also asynchronous in a single thread, but in nodejs you run all users in one thread whereas in browser JavaScript you get a thread per user (each browser instance). nodejs may look easy, because it is just JavaScript, but it has these subtle parts that you need to be aware of even as a beginner.