Asynchronous Callback Javascript With Complex Calculation

Question

I'm trying to do some calculation asynchronously and get the result from the calculation in the callback.

function customWithCallBack(callback) {
 //Complex logic calculation that takes time.
   callback();
}

function actualCallBack() {
 console.log("This is callback called after certain event");
}


console.log("First");
customWithCallBack(actualCallBack);
console.log("Second");

//Required Output
First
Second
This is callback called after certain event.


//Actual Output
First
This is callback called after certain event
Second

How can I achieve the required output? That is first "First is printed". Then, "Second". And at last after the completion of complex logic callback is called to print "This is callback called after certain event". Is it possible to do it for complex calculations except network req and i/o operations?

This is quite a similar question to this link: https://stackoverflow.com/questions/9516900/how-can-i-create-an-asynchronous-function-in-javascript — Geono, Jun 21 '17 at 07:50

score 1 · Accepted Answer · answered Jun 21 '17 at 07:38

1

function customWithCallBack(callback) {
 //Complex logic calculation that takes time.
     setTimeout(function(){ callback(); }, 100);
   
}

function actualCallBack() {
 console.log("This is callback called after certain event");
}


console.log("First");
customWithCallBack(actualCallBack);
console.log("Second");

answered Jun 21 '17 at 07:38

Gaurav joshi

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callback() is called after 100 ms... what i want is to execute callback after the complex logic calculations... how can we achieve that? – xerox007 Jun 21 '17 at 07:43
Call callback After ur calculation gets complete – Gaurav joshi Jun 21 '17 at 09:03

score 0 · Answer 2 · answered Jun 21 '17 at 07:43

So you want to end the current callstack, then start a new callstack with your callback. This can be achieved through pushing callback onto the qeue, the qeue contains all triggered event handlers and timers and it starts new callstacks one after another. So you can do:

setTimeout(callback,0,"param1","param2");

So callback is executed after the current callstack ends.

score 0 · Answer 3 · answered Sep 24 '18 at 12:13

I was a little inspired by this question, because I hit a similar problem some time ago once I've tried to compute large array. It's a combination of solution that uses setTimeout with chunking operation (so that execution will not block entire thread). Here you can see a package created: https://www.npmjs.com/package/chunked-call

Asynchronous Callback Javascript With Complex Calculation

3 Answers3