Discussion on: Understanding the Node.js event loop phases and how it executes the JavaScript code.

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Hello nice article. I have clarifying question process.nextTick() happens after all the event loop phases or before the phases?

Sumedh Nimkarde • Feb 11 '20

Hi, process.nextTick callbacks are executed immediately. As mentioned, whenever the event loop encounters process.nextTick, it finishes its current callback execution(no matter what phase it is in), then pauses and executes our process.nextTick callback first after which it resumes to the phase which it left its work on.

I hope you this answers your question.

aRtoo • Feb 11 '20

Thank you for the response sir. Last question it only happens in their execution context right? say I have this code:

console.log('bar')

function f() {
 process.nextTick(console.log('foo'))
}

f()
setImmediate( ()=> console.log('immediate') )

output:
bar
immediate
foo

even though I called f() first before setImmediate

Sumedh Nimkarde • Feb 13 '20

Hey, pardon for the late reply. Yes, it happens in the execution context. Thanks for reminding, I think I forgot to mention this term in the article! By the way, I think you may have mistaken for the output, after executing, the output seems to be:

bar
foo
immediate

Here is how it happens:

console.log gets logged
f is called. f()
now, everything happens according to the f() context. i.e process.nextTick will execute with priority. If there are any other setTimeout, setImmediate callbacks, they will be pushed to the respective queues and executed.
lastly, when the function returns, we come back to the last setImmediate, and execute the callback.

aRtoo • Feb 14 '20

I never tried my code. I thought process.nextTick will be push to event loop and setImmediate will run next since its in the higher or outer execution context.

anyway thanks for explaining. :)

kausachan • Jan 28 '23 • Edited

Every code gets executed inside execution context only right? then why that question was raised? Am I not understanding something? pls help!