async Callback in for loop Fail

Question

I am writing a Node JS function which have array of objects and for each item of it I need to call async function

for (var i = 0; i < allCases.length; i++) {

    if (allCases[i].Case_ID != null) {
        Utils.findAndUpdate(allCases[i], function(response) {
            console.log('received in the callback ', response);
        });
    } else {
        console.log('case id is null');
    }
}

findAndUpdate is a function which executes async calls and return the result in the callback. when i tried this on a single item it worked perfectly but within the loop it fails as the loop step over and reach the end while the callback is still happening.

i also tried this workaround to only increase the ' i ' in the callback success. but it leads to infinite loop

for (let i = 0; i < allCases.length;) {

    if (allCases[i].Case_ID != null) {
        Utils.findAndUpdate(allCases[i], function(response) {
            console.log('received in the callback ', response);
            i++;
        });
    } else {
        console.log('case id is null');
    }
}

i wonder how to solve this and why this workaround failed.

Ivan Minakov · Accepted Answer · 2017-08-17 11:09:36Z

2

Try this instead:

allCases.forEach((case) => {
  if (case.Case_ID != null) {
      Utils.findAndUpdate(case, function (response) {
        console.log('received in the callback ', response);
      });
    } else {
      console.log('case id is null');
    }
  });

But if you want to chain requests, then you should should get rid of cycles

edited Aug 17, 2017 at 11:09

answered Aug 17, 2017 at 11:03

Ivan Minakov

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1 Comment

Mohamed A. Shebl Over a year ago

Thanks it worked. more explanation would be appreciated to your answer demonstrating why this approach worked. i also have a question how i would determine that i reached the last callback in the thread ?

RIYAJ KHAN · Accepted Answer · 2017-08-17 11:13:39Z

2

You can use IIFE;

for (let i = 0; i < allCases.length;) {

    if (allCases[i].Case_ID != null) {
        (function (i) {
            Utils.findAndUpdate(allCases[i], function (response) {
                console.log('received in the callback ', response);
            });
        })(i)

    } else {
        console.log('case id is null');
    }
  i++;
}

answered Aug 17, 2017 at 11:13

RIYAJ KHAN

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2 Comments

Mohamed A. Shebl Over a year ago

Thanks this also worked. i also have a question how i could determine that i reached the last callback in the thread ?

RIYAJ KHAN Over a year ago

check the value of i should be equal to length-1

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