It waits in a queue in a background thread in the node.js http library until your code can execute to handle it. So if your code takes a long time before return

It waits in a queue in a background thread in the node.js http library until your code can execute to handle it. So if your code takes a long time before returning back to the event loop the request will just wait in that queue for a long time before the next opportunity for the event loop to execute code in response to the event.