JavaScript Multiple Callback Function

Question

I have been trying to figure out the Callback function feature in Javascript for a while without any success. I probably have the code messed up, however I am not getting any Javascript errors, so I supposed the syntax is somewhat correct.

Basically, I am looking for the getDistanceWithLatLong() function to end before the updateDB() begins, and then make sure that ends before the printList() function begins.

I have it working with a hardcoded "setTimeout" call on the functions, but I am overcompensating and forcing users to wait longer without a need if the Callback stuff would work.

Any suggestions? Below is the code:

function runSearchInOrder(callback) {
    getDistanceWithLatLong(function() {
        updateDB(function() {
            printList(callback);
        });
    });
}

Ignoring the problem about multiple callbacks, what are you trying to accomplish? — Matthew
– Matthew, Commented May 20, 2014 at 0:39
I need the following 3 functions to run and finish in order: getDistanceWithLatLong(); updateDB(); printList(): Just listing them that way I would have thought would work, but when i print things in the console.log sometimes the printList() runs before the loops of the other function is done. — Rob
– Rob, Commented May 20, 2014 at 0:40
Are the getDistance... and updatedDB functions expecting a callback? I do not see why it wouldn't work if they do. — plalx
– plalx, Commented May 20, 2014 at 1:17

000 · Accepted Answer · 2014-05-20 00:42:23Z

27

To accomplish this, you need to pass the next callback into each function.

function printList(callback) {
  // do your printList work
  console.log('printList is done');
  callback();
}

function updateDB(callback) {
  // do your updateDB work
  console.log('updateDB is done');
  callback()
}

function getDistanceWithLatLong(callback) {
  // do your getDistanceWithLatLong work
  console.log('getDistanceWithLatLong is done');
  callback();
}

function runSearchInOrder(callback) {
    getDistanceWithLatLong(function() {
        updateDB(function() {
            printList(callback);
        });
    });
}

runSearchInOrder(function(){console.log('finished')});

This code outputs:

getDistanceWithLatLong is done
updateDB is done
printList is done
finished

answered May 20, 2014 at 0:42

000

27.3k10 gold badges74 silver badges103 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

RaduS Over a year ago

what about what passing variables from one callback to another?

Yamcha · Accepted Answer · 2017-02-14 22:00:24Z

1

wouldn't this work:

function callback(f1, f2) {
    f1();
    f2();
}

As for passing arguments, be creative.

answered Feb 14, 2017 at 22:00

Yamcha

1,3441 gold badge19 silver badges24 bronze badges

Comments

Renji Joseph Sabu Niravath · Accepted Answer · 2020-01-16 19:25:29Z

function1 = (callback1, callback2, callback3) => {
  setTimeout(() => {
    console.log("function 1 timed out!");
    callback1(callback2, callback3);
  }, 1500);
}

function2 = (callback1, callback2) => {
  setTimeout(() => {
    console.log("function 2 timed out!");
    callback1(callback2);
  }, 1500);
}

function3 = (callback1) => {
  setTimeout(() => {
    console.log("function 3 timed out!")
    callback1()
  }, 1500);
}

function4 = () => {
  setTimeout(() => {
    console.log("function 4 timed out!")
  }, 1500);
}

function1(function2, function3, function4);

Just pass down the callbacks from the first function and execute each one, passing down the rest.

OUTPUT

function 1 timed out!
function 2 timed out!
function 3 timed out!
function 4 timed out!

gregnr · Accepted Answer · 2014-05-20 00:46:46Z

0

In JavaScript, everything is an object, including functions. That is why you are able to pass callbacks as parameters - you are passing a function as if it were any other object.

In each function declaration, you need to run the callback.

function runSearchInOrder(callback) {

    ...

    callback();
}

function getDistanceWithLatLong(callback) {

    ...

    callback();
}

function updateDB(callback) {

    ...

    callback();
}

Then your code posted above should work.

answered May 20, 2014 at 0:46

gregnr

1,2728 silver badges11 bronze badges

Collectives™ on Stack Overflow

JavaScript Multiple Callback Function

4 Answers 4

1 Comment

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

1 Comment

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related