How to return from the inner callback, in the below scenario, a json data is being return, when i try to do console.log it print the [Function] instead of json value

exports.tests = function(tagName, out) {

    model.findbyTag(tagName, function(data) {

        var json = {
            "name" : 'java',
            "data" : "SomeData"
        }

        return json;

    });

}

console.log(this.tests)

it output

[Function]

What wrong i'm doing so that when this method execute it should return the json data

How to return from the inner callback, in the below scenario, a json data is being return, when i try to do console.log it print the [Function] instead of json value

exports.tests = function(tagName, out) {

    model.findbyTag(tagName, function(data) {

        var json = {
            "name" : 'java',
            "data" : "SomeData"
        }

        return json;

    });

}

console.log(this.tests)

it output

[Function]

What wrong i'm doing so that when this method execute it should return the json data

• javascript
• json
• node.js

• you can't return data from a callback – dandavis Commented Oct 30, 2014 at 7:59
• is there any way to log the json when finshed processing – anish Commented Oct 30, 2014 at 8:01
• sure, simply replace "return json" with "console.log(json)" – dandavis Commented Oct 30, 2014 at 8:02
• from the calling function, other module will use this data – anish Commented Oct 30, 2014 at 8:03
• no it won't, unless you give the other module to the callback. in async, you need to take the action to the data instead of the traditional approach of taking the data to the action. – dandavis Commented Oct 30, 2014 at 8:04

3 Answers 3

module.exports = function() {

    var _return  = {};

    _return.someName = function(tagName ,callback){
        model.findbyTag(tagName, function(err ,data) {
            var json = {
                "name" : 'java',
                "data" : "SomeData"
            }
            callback(json);
        });
    }

    return _return ;
}

You can use above code like this in another file :

var sample_file = require('above code file address');

sample_file.someName(someTagName , function (data) {
    console.log(data) // this data is the json data
})

You can't return data from a callback, instead you should pass a function into the method that can be called inside the callback with the result.

Example :

exports.tests = function(tagName, out, returnFunction) {

    model.findbyTag(tagName, function(data) {

        var json = {
            "name" : 'java',
            "data" : "SomeData"
        }
        // Call the returnFunction instead of trying to return data
        returnFunction(json);

    });

}

And then call it as so :

this.tests('tagName', 'out', function(r) {
    // Where "r" is the result of the callback
    console.log(r);
});

You need to use Node emitter for that, if you use Node in the first place of course.

const EventEmitter = require('events');

class MyEmitter extends EventEmitter {}

const myEmitter = new MyEmitter();
myEmitter.on('event', (someProps) => {
  console.log('an event occurred!');
});
myEmitter.emit('event', {...someProps});

Then you can access the json and call any further actions that is required. Working with events might make you to restructure your application slightly. https://nodejs/docs/latest/api/events.html#events_emitter_on_eventname_listener