Use callback with javascript

Question

I am creating project using javascript and nodejs. I am integrating callback in my function inside for loop with condition basis,but am unable to do this.my problem is callback is completed on first iteration of loop. here is my code:

function tagEndpointNames(callback) {

    var data = userGenerateToken();
    var sql = "SELECT * FROM topology_data WHERE topology_coordinates !='' and topology_uuid is not null"

    var query = conn.query(sql, function(err, tagEndpointNames) {

        for (var i = 0; i < tagEndpointNames.length; i++) {
            var topologytagData = {
                "topology_tag": tagEndpointNames[i].topology_uuid
            }

            var tpCooridinates = JSON.parse(tagEndpointNames[i].topology_coordinates);

            for (var j = 0; j < tpCooridinates.stageObjects.length; j++) {

                if (tpCooridinates.stageObjects.length) {

                    if (tpCooridinates.stageObjects[j].endPointId) {

                        if (isGuid(tpCooridinates.stageObjects[j].endPointId)) {

                            var endPointUUID = tpCooridinates.stageObjects[j].endPointId;
                            var _ro = require('request');

                            var url = url;

                            var _d = '';

                            _ro({
                                url: url,
                                method: 'POST',
                                headers: {
                                    'Content-Type': 'application/json',
                                    'Authorization': 'Bearer ' + data['access_token']
                                },

                                json: topologytagData

                            }, function(_e, _r, _b) {

                                if (_r.statusCode == 200 && !_e) {

                                    callback()
                                        //return;
                                } else {

                                    callback()
                                    console.log("andarss")
                                    return;
                                }

                            })
                        }
                    }
                }
            }
        }

    })
}

Here is the function call:

tagEndpointNames(function(){
            console.log ('Server Closed during MIGRATION JOB 4');
            server.close(function () {
                process.exit(0);
            });
        })

your code formatting makes my brain bleed when I try to read it — Jaromanda X
– Jaromanda X, Commented Nov 28, 2016 at 5:46
url is the url where request is go am just temporary write url — Karan
– Karan, Commented Nov 28, 2016 at 6:15
Please run your code through JS lint and fix missing semicolons at ends of lines. I noticed at least two. — user6269864
– user6269864, Commented Nov 28, 2016 at 6:41

Community · Accepted Answer · 2017-05-23 11:45:57Z

0

When you are running asynchronous process with callback in a for loop, remember that the callback from callee will be fired in the first event completed inside the loop. In your case request lib call is an asynchronous process inside for loop, you need to handle all callback from all the request call before you want to callback the callee.

Please read: How to write asynchronous functions for Node.js

edited May 23, 2017 at 11:45

CommunityBot

11 silver badge

answered Nov 28, 2016 at 5:49

iKoala

8804 silver badges11 bronze badges

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

Comments

Giovanni Lobitos · Accepted Answer · 2016-11-28 06:16:34Z

0

Maybe it's time for you to start using Javascript Promise.

answered Nov 28, 2016 at 6:16

Giovanni Lobitos

8527 silver badges19 bronze badges

Comments

Community · Accepted Answer · 2017-05-23 12:13:50Z

The async library for Node will help you for doing this kind of tasks.

Use async waterfall.It Runs an array of functions in series, each passing their results to the next in the array. However, if any of the functions pass an error to the callback, the next function is not executed and the main callback is immediately called with the error.

js

var create = function (req, res) {
    async.waterfall([
        _function1(req),
        _function2,
        _function3
    ], function (error, success) {
        if (error) { alert('Something is wrong!'); }
        return alert('Done!');
    });
};

function _function1 (req) {
    return function (callback) {
        var something = req.body;
        callback (null, something);
   }
}

function _function2 (something, callback) {
    return function (callback) {
       var somethingelse = function () { // do something here };
       callback (err, somethingelse);
    }
}

function _function3 (something, callback) {
    return function (callback) {
      var somethingmore = function () { // do something here };
      callback (err, somethingmore);
    }
}

Reference

Collectives™ on Stack Overflow

Use callback with javascript

3 Answers 3

Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related