How to handle asynchronous callbacks within an if - else statement?

Question

For a project I need to alter some values in a file in five if-statements that are executed one after another, and after all those things are done, I need to save the file. One of the alteration contains an asynchronous save image function. The problem I'm having is that that function has not finished by the time the program gets to the file writing. How should I handle the callbacks within the if-statement? The save image function should be executed before the program proceeds to the next if statement.

if(criterium1){... //Alter file}

if(criterium2){
    saveImage(searchValue, folder,callback(error)){
        ... //Alter file
    }
if(criterium3){... //Alter file}

fs.writeFile(opfFile, xml, function(error) {
    callback(null);
 });

 var saveImage = function(searchValue, folder, callback){
    var images = require ('google-images2');
    images.search(searchValue, function(error, image){
        callback(null);
    });
 };

Can anyone give me any pointer on how to handle this? Thanks! Kind regards, Eva

Community · Accepted Answer · 2020-06-20 09:12:55Z

4

as Transcendence said, async is really good for that kind of flow.

I just wrote a simple async-if-else module, because I had a similar problem on my chain steps.

async.waterfall([
   async.if(criterium1, fnCriterium1),
   async.if(criterium2, fnCriterium2),
   async.if(criterium3, fnCriterium3).else(fnCriteriumAlternative)
 ], handler);

I hope this could help you !

cheers

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Oct 23, 2015 at 15:08

CHAPa

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Comments

sigod · Accepted Answer · 2017-07-28 04:22:18Z

1

You can use the async library, specifically its series control flow. https://caolan.github.io/async/docs.html#series

You want to execute your if statements as tasks in the array (first argument). Make sure to call the callback when your asynchronous actions are done. The second argument is a callback that will execute when all your tasks are done.

async.series([
    function(callback){
        if(criterium1) {
          //Alter file
          // make sure to call the callback
        } else {
          callback(null, null);
        }
    },
    function(callback){
        if(criterium2) {
          //Alter file
          // make sure to call the callback
          // looks like you can just pass callback into the saveImage function
        } else {
          callback(null, null);
        }
    }
], function () {
  fs.writeFile(opfFile, xml, function(error) {
    callback(null);
 });
});

edited Jul 28, 2017 at 4:22

sigod

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answered Apr 25, 2015 at 8:41

Transcendence

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6 Comments

Eva Over a year ago

But it's possible that the second statement won't be executed, so then the third statement and the writeFile will not be executed, right?

Transcendence Over a year ago

I am having trouble understanding your example code due to extraneous braces.

Eva Over a year ago

I'm sorry. Is this better?

Transcendence Over a year ago

lemme alter my answer

Transcendence Over a year ago

sorry that took a while

|

Sathish · Accepted Answer · 2015-04-25 10:18:17Z

0

Try wrapping all functions inside a promise

answered Apr 25, 2015 at 10:18

Sathish

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