CODEWITHSUNDEEP
javascript
user1400915
user1400915

Reputation: 1943

Callback queue in case of synchronous callback

I understand that the asynchronous callback function will be pushed into the callback queue. For eg:

setTimeout(function() {
   console.log('Async');
}, 0);

In the above case, the callback function is pushed into the callback queue.

Will the synchronous callback function will also be pushed into the callback queue?

function a(b)
{
 console.log('First function')
}

a(function b()
{
console.log('Sync Callback')
});
will the function b will also be pushed into the callback queue?

Upvotes: 0

Views: 297

Answers (1)

Olian04
Olian04

Reputation: 6872

will function b also be pushed onto the callback queue?

Short answer: NO.

Slightly longer answer: In your second snippet you are passing function b as an argument to function a, this happens synchronously. However you're never using function b inside function a, so while function a will evaluate, function b will neither be put on the queue, nor evaluated.

If you wanted b to be evaluated emediatly you would need to call it inside of a:

function a(arg_b) {
  arg_b();
  console.log('First function')
}

a(function b() {
  console.log('Sync Callback')
});

If you instead wanted b to be put on the queue and evaluated at a later point, you would need to create a task (or a microtask):

function a(arg_b) {
  setTimeout(arg_b, 0);
  console.log('First function')
}

a(function b() {
  console.log('Sync Callback')
});

Upvotes: 1

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