Node.js event loop understanding (with a diagram)
The diagram does seem quite complicated. I find a king analogy quite perfect in this context to have a grey level understanding about how event-loop works.
Imagine the code you want to run is a king and node is the army of servants.
The day starts by one servant waking up the king and asking him if he needs anything. The king gives the servant a list of tasks and goes back to sleep a little longer. The servant now distributes those tasks among his colleagues and they get to work.
Once a servant finishes a task, he lines up outside the kings quarter to report. The king lets one servant in at a time, and listens to things he reports. Sometimes the king will give the servant more tasks on the way out.
Life is good, for the king's servants carry out all of his tasks in parallel, but only report with one result at a time, so the king can focus.
The king here is the main node process. This is how the nodejs is said to be single-threaded yet asynchronous.