Callback executed too early












1














I'm struggling with an issue I can't get around.



I'm using NodeJS to request data from Rest API´s. For this program I first retrieve an array of data, then I request some details from another endpoint based on an id from the first array.



I use a foreach loop inside the first function call with callback, and then another function call within the foreach loop to get the details.



What I experience is that the second function does callback before the response is retrieved.



I have managed to reproduce the issue with the following example code:



console.log('Program start')



// Executing program

getFirstname(function(person) {



    person.forEach(firstname => {



        getSurname(firstname.id, function(lastname) {

            console.log(`${firstname.value} ${lastname}`)

        });



    });

})



// Emulating REST API´s

function getFirstname(callback) {



    console.log('Returning list of firstnames')



    let data = [

        {id: 0, value: 'John'},

        {id: 2, value: 'Andy'},

        {id: 3, value: 'Jimmy'},

        {id: 4, value: 'Alex'},

        {id: 0, value: 'John'},

        {id: 2, value: 'Andy'},

        {id: 3, value: 'Jimmy'},

        {id: 4, value: 'Alex'},

        {id: 0, value: 'John'},

        {id: 2, value: 'Andy'},

        {id: 3, value: 'Jimmy'},

        {id: 4, value: 'Alex'},

        {id: 0, value: 'John'},

        {id: 2, value: 'Andy'},

        {id: 3, value: 'Jimmy'},

        {id: 4, value: 'Alex'},

        {id: 0, value: 'John'},

        {id: 2, value: 'Andy'},

        {id: 3, value: 'Jimmy'},

        {id: 4, value: 'Alex'},

        {id: 0, value: 'John'},

        {id: 2, value: 'Andy'},

        {id: 3, value: 'Jimmy'},

        {id: 4, value: 'Alex'},

        {id: 0, value: 'John'},

        {id: 2, value: 'Andy'},

        {id: 3, value: 'Jimmy'},

        {id: 4, value: 'Alex'},

        {id: 0, value: 'John'},

        {id: 2, value: 'Andy'},

        {id: 3, value: 'Jimmy'},

        {id: 4, value: 'Alex'},

        {id: 0, value: 'John'},

        {id: 2, value: 'Andy'},

        {id: 3, value: 'Jimmy'},

        {id: 4, value: 'Alex'},

        {id: 0, value: 'John'},

        {id: 2, value: 'Andy'},

        {id: 3, value: 'Jimmy'},

        {id: 4, value: 'Alex'},

    ]



    callback(data);

}



function getSurname(id, callback) {



    console.log(`Querying for lastname id ${id}`)



    let data = [

        'Andersen',

        'Johsen',

        'Falon',

        'Alexander',

    ]



    setTimeout(() => {

        callback(data[id]);

    }, 2000);

}


Here is the result of the program:



Program start

Returning list of firstnames

Querying for lastname id 0

Querying for lastname id 2

Querying for lastname id 3

Querying for lastname id 4

Querying for lastname id 0

Querying for lastname id 2

Querying for lastname id 3

Querying for lastname id 4

Querying for lastname id 0

Querying for lastname id 2

Querying for lastname id 3

Querying for lastname id 4

Querying for lastname id 0

Querying for lastname id 2

Querying for lastname id 3

Querying for lastname id 4

Querying for lastname id 0

Querying for lastname id 2

Querying for lastname id 3

Querying for lastname id 4

Querying for lastname id 0

Querying for lastname id 2

Querying for lastname id 3

Querying for lastname id 4

Querying for lastname id 0

Querying for lastname id 2

Querying for lastname id 3

Querying for lastname id 4

Querying for lastname id 0

Querying for lastname id 2

Querying for lastname id 3

Querying for lastname id 4

Querying for lastname id 0

Querying for lastname id 2

Querying for lastname id 3

Querying for lastname id 4

Querying for lastname id 0

Querying for lastname id 2

Querying for lastname id 3

Querying for lastname id 4

John Andersen

Andy Falon

Jimmy Alexander

Alex undefined

John Andersen

Andy Falon

Jimmy Alexander

Alex undefined

John Andersen

Andy Falon

Jimmy Alexander

Alex undefined

John Andersen

Andy Falon

Jimmy Alexander

Alex undefined

John Andersen

Andy Falon

Jimmy Alexander

Alex undefined

John Andersen

Andy Falon

Jimmy Alexander

Alex undefined

John Andersen

Andy Falon

Jimmy Alexander

Alex undefined

John Andersen

Andy Falon

Jimmy Alexander

Alex undefined

John Andersen

Andy Falon

Jimmy Alexander

Alex undefined

John Andersen

Andy Falon

Jimmy Alexander

Alex undefined


As you can see, there are several records with undefined value. Also I have added a setTimeout to emulate that each rest call takes a few seconds. What happens is that all the queries are fired off instantly, then it goes 2 seconds before all the responses return simultaneous.



I would expect this to wait for each second rest call and then return the result.



How can I solve this issue?



Best regards,
Christian






javascript node.js loops foreach callback







share|improve this question





























    1














    I'm struggling with an issue I can't get around.



    I'm using NodeJS to request data from Rest API´s. For this program I first retrieve an array of data, then I request some details from another endpoint based on an id from the first array.



    I use a foreach loop inside the first function call with callback, and then another function call within the foreach loop to get the details.



    What I experience is that the second function does callback before the response is retrieved.



    I have managed to reproduce the issue with the following example code:



    console.log('Program start')
    

    
// Executing program
    
getFirstname(function(person) {
    

    
    person.forEach(firstname => {
    

    
        getSurname(firstname.id, function(lastname) {
    
            console.log(`${firstname.value} ${lastname}`)
    
        });
    

    
    });
    
})
    

    
// Emulating REST API´s
    
function getFirstname(callback) {
    

    
    console.log('Returning list of firstnames')
    

    
    let data = [
    
        {id: 0, value: 'John'},
    
        {id: 2, value: 'Andy'},
    
        {id: 3, value: 'Jimmy'},
    
        {id: 4, value: 'Alex'},
    
        {id: 0, value: 'John'},
    
        {id: 2, value: 'Andy'},
    
        {id: 3, value: 'Jimmy'},
    
        {id: 4, value: 'Alex'},
    
        {id: 0, value: 'John'},
    
        {id: 2, value: 'Andy'},
    
        {id: 3, value: 'Jimmy'},
    
        {id: 4, value: 'Alex'},
    
        {id: 0, value: 'John'},
    
        {id: 2, value: 'Andy'},
    
        {id: 3, value: 'Jimmy'},
    
        {id: 4, value: 'Alex'},
    
        {id: 0, value: 'John'},
    
        {id: 2, value: 'Andy'},
    
        {id: 3, value: 'Jimmy'},
    
        {id: 4, value: 'Alex'},
    
        {id: 0, value: 'John'},
    
        {id: 2, value: 'Andy'},
    
        {id: 3, value: 'Jimmy'},
    
        {id: 4, value: 'Alex'},
    
        {id: 0, value: 'John'},
    
        {id: 2, value: 'Andy'},
    
        {id: 3, value: 'Jimmy'},
    
        {id: 4, value: 'Alex'},
    
        {id: 0, value: 'John'},
    
        {id: 2, value: 'Andy'},
    
        {id: 3, value: 'Jimmy'},
    
        {id: 4, value: 'Alex'},
    
        {id: 0, value: 'John'},
    
        {id: 2, value: 'Andy'},
    
        {id: 3, value: 'Jimmy'},
    
        {id: 4, value: 'Alex'},
    
        {id: 0, value: 'John'},
    
        {id: 2, value: 'Andy'},
    
        {id: 3, value: 'Jimmy'},
    
        {id: 4, value: 'Alex'},
    
    ]
    

    
    callback(data);
    
}
    

    
function getSurname(id, callback) {
    

    
    console.log(`Querying for lastname id ${id}`)
    

    
    let data = [
    
        'Andersen',
    
        'Johsen',
    
        'Falon',
    
        'Alexander',
    
    ]
    

    
    setTimeout(() => {
    
        callback(data[id]);
    
    }, 2000);
    
}


    Here is the result of the program:



    Program start
    
Returning list of firstnames
    
Querying for lastname id 0
    
Querying for lastname id 2
    
Querying for lastname id 3
    
Querying for lastname id 4
    
Querying for lastname id 0
    
Querying for lastname id 2
    
Querying for lastname id 3
    
Querying for lastname id 4
    
Querying for lastname id 0
    
Querying for lastname id 2
    
Querying for lastname id 3
    
Querying for lastname id 4
    
Querying for lastname id 0
    
Querying for lastname id 2
    
Querying for lastname id 3
    
Querying for lastname id 4
    
Querying for lastname id 0
    
Querying for lastname id 2
    
Querying for lastname id 3
    
Querying for lastname id 4
    
Querying for lastname id 0
    
Querying for lastname id 2
    
Querying for lastname id 3
    
Querying for lastname id 4
    
Querying for lastname id 0
    
Querying for lastname id 2
    
Querying for lastname id 3
    
Querying for lastname id 4
    
Querying for lastname id 0
    
Querying for lastname id 2
    
Querying for lastname id 3
    
Querying for lastname id 4
    
Querying for lastname id 0
    
Querying for lastname id 2
    
Querying for lastname id 3
    
Querying for lastname id 4
    
Querying for lastname id 0
    
Querying for lastname id 2
    
Querying for lastname id 3
    
Querying for lastname id 4
    
John Andersen
    
Andy Falon
    
Jimmy Alexander
    
Alex undefined
    
John Andersen
    
Andy Falon
    
Jimmy Alexander
    
Alex undefined
    
John Andersen
    
Andy Falon
    
Jimmy Alexander
    
Alex undefined
    
John Andersen
    
Andy Falon
    
Jimmy Alexander
    
Alex undefined
    
John Andersen
    
Andy Falon
    
Jimmy Alexander
    
Alex undefined
    
John Andersen
    
Andy Falon
    
Jimmy Alexander
    
Alex undefined
    
John Andersen
    
Andy Falon
    
Jimmy Alexander
    
Alex undefined
    
John Andersen
    
Andy Falon
    
Jimmy Alexander
    
Alex undefined
    
John Andersen
    
Andy Falon
    
Jimmy Alexander
    
Alex undefined
    
John Andersen
    
Andy Falon
    
Jimmy Alexander
    
Alex undefined


    As you can see, there are several records with undefined value. Also I have added a setTimeout to emulate that each rest call takes a few seconds. What happens is that all the queries are fired off instantly, then it goes 2 seconds before all the responses return simultaneous.



    I would expect this to wait for each second rest call and then return the result.



    How can I solve this issue?



    Best regards,
    Christian






    javascript node.js loops foreach callback







    share|improve this question



























      1












      1








      1







      I'm struggling with an issue I can't get around.



      I'm using NodeJS to request data from Rest API´s. For this program I first retrieve an array of data, then I request some details from another endpoint based on an id from the first array.



      I use a foreach loop inside the first function call with callback, and then another function call within the foreach loop to get the details.



      What I experience is that the second function does callback before the response is retrieved.



      I have managed to reproduce the issue with the following example code:



      console.log('Program start')
      

      
// Executing program
      
getFirstname(function(person) {
      

      
    person.forEach(firstname => {
      

      
        getSurname(firstname.id, function(lastname) {
      
            console.log(`${firstname.value} ${lastname}`)
      
        });
      

      
    });
      
})
      

      
// Emulating REST API´s
      
function getFirstname(callback) {
      

      
    console.log('Returning list of firstnames')
      

      
    let data = [
      
        {id: 0, value: 'John'},
      
        {id: 2, value: 'Andy'},
      
        {id: 3, value: 'Jimmy'},
      
        {id: 4, value: 'Alex'},
      
        {id: 0, value: 'John'},
      
        {id: 2, value: 'Andy'},
      
        {id: 3, value: 'Jimmy'},
      
        {id: 4, value: 'Alex'},
      
        {id: 0, value: 'John'},
      
        {id: 2, value: 'Andy'},
      
        {id: 3, value: 'Jimmy'},
      
        {id: 4, value: 'Alex'},
      
        {id: 0, value: 'John'},
      
        {id: 2, value: 'Andy'},
      
        {id: 3, value: 'Jimmy'},
      
        {id: 4, value: 'Alex'},
      
        {id: 0, value: 'John'},
      
        {id: 2, value: 'Andy'},
      
        {id: 3, value: 'Jimmy'},
      
        {id: 4, value: 'Alex'},
      
        {id: 0, value: 'John'},
      
        {id: 2, value: 'Andy'},
      
        {id: 3, value: 'Jimmy'},
      
        {id: 4, value: 'Alex'},
      
        {id: 0, value: 'John'},
      
        {id: 2, value: 'Andy'},
      
        {id: 3, value: 'Jimmy'},
      
        {id: 4, value: 'Alex'},
      
        {id: 0, value: 'John'},
      
        {id: 2, value: 'Andy'},
      
        {id: 3, value: 'Jimmy'},
      
        {id: 4, value: 'Alex'},
      
        {id: 0, value: 'John'},
      
        {id: 2, value: 'Andy'},
      
        {id: 3, value: 'Jimmy'},
      
        {id: 4, value: 'Alex'},
      
        {id: 0, value: 'John'},
      
        {id: 2, value: 'Andy'},
      
        {id: 3, value: 'Jimmy'},
      
        {id: 4, value: 'Alex'},
      
    ]
      

      
    callback(data);
      
}
      

      
function getSurname(id, callback) {
      

      
    console.log(`Querying for lastname id ${id}`)
      

      
    let data = [
      
        'Andersen',
      
        'Johsen',
      
        'Falon',
      
        'Alexander',
      
    ]
      

      
    setTimeout(() => {
      
        callback(data[id]);
      
    }, 2000);
      
}


      Here is the result of the program:



      Program start
      
Returning list of firstnames
      
Querying for lastname id 0
      
Querying for lastname id 2
      
Querying for lastname id 3
      
Querying for lastname id 4
      
Querying for lastname id 0
      
Querying for lastname id 2
      
Querying for lastname id 3
      
Querying for lastname id 4
      
Querying for lastname id 0
      
Querying for lastname id 2
      
Querying for lastname id 3
      
Querying for lastname id 4
      
Querying for lastname id 0
      
Querying for lastname id 2
      
Querying for lastname id 3
      
Querying for lastname id 4
      
Querying for lastname id 0
      
Querying for lastname id 2
      
Querying for lastname id 3
      
Querying for lastname id 4
      
Querying for lastname id 0
      
Querying for lastname id 2
      
Querying for lastname id 3
      
Querying for lastname id 4
      
Querying for lastname id 0
      
Querying for lastname id 2
      
Querying for lastname id 3
      
Querying for lastname id 4
      
Querying for lastname id 0
      
Querying for lastname id 2
      
Querying for lastname id 3
      
Querying for lastname id 4
      
Querying for lastname id 0
      
Querying for lastname id 2
      
Querying for lastname id 3
      
Querying for lastname id 4
      
Querying for lastname id 0
      
Querying for lastname id 2
      
Querying for lastname id 3
      
Querying for lastname id 4
      
John Andersen
      
Andy Falon
      
Jimmy Alexander
      
Alex undefined
      
John Andersen
      
Andy Falon
      
Jimmy Alexander
      
Alex undefined
      
John Andersen
      
Andy Falon
      
Jimmy Alexander
      
Alex undefined
      
John Andersen
      
Andy Falon
      
Jimmy Alexander
      
Alex undefined
      
John Andersen
      
Andy Falon
      
Jimmy Alexander
      
Alex undefined
      
John Andersen
      
Andy Falon
      
Jimmy Alexander
      
Alex undefined
      
John Andersen
      
Andy Falon
      
Jimmy Alexander
      
Alex undefined
      
John Andersen
      
Andy Falon
      
Jimmy Alexander
      
Alex undefined
      
John Andersen
      
Andy Falon
      
Jimmy Alexander
      
Alex undefined
      
John Andersen
      
Andy Falon
      
Jimmy Alexander
      
Alex undefined


      As you can see, there are several records with undefined value. Also I have added a setTimeout to emulate that each rest call takes a few seconds. What happens is that all the queries are fired off instantly, then it goes 2 seconds before all the responses return simultaneous.



      I would expect this to wait for each second rest call and then return the result.



      How can I solve this issue?



      Best regards,
      Christian






      javascript node.js loops foreach callback







      share|improve this question















      I'm struggling with an issue I can't get around.



      I'm using NodeJS to request data from Rest API´s. For this program I first retrieve an array of data, then I request some details from another endpoint based on an id from the first array.



      I use a foreach loop inside the first function call with callback, and then another function call within the foreach loop to get the details.



      What I experience is that the second function does callback before the response is retrieved.



      I have managed to reproduce the issue with the following example code:



      console.log('Program start')
      

      
// Executing program
      
getFirstname(function(person) {
      

      
    person.forEach(firstname => {
      

      
        getSurname(firstname.id, function(lastname) {
      
            console.log(`${firstname.value} ${lastname}`)
      
        });
      

      
    });
      
})
      

      
// Emulating REST API´s
      
function getFirstname(callback) {
      

      
    console.log('Returning list of firstnames')
      

      
    let data = [
      
        {id: 0, value: 'John'},
      
        {id: 2, value: 'Andy'},
      
        {id: 3, value: 'Jimmy'},
      
        {id: 4, value: 'Alex'},
      
        {id: 0, value: 'John'},
      
        {id: 2, value: 'Andy'},
      
        {id: 3, value: 'Jimmy'},
      
        {id: 4, value: 'Alex'},
      
        {id: 0, value: 'John'},
      
        {id: 2, value: 'Andy'},
      
        {id: 3, value: 'Jimmy'},
      
        {id: 4, value: 'Alex'},
      
        {id: 0, value: 'John'},
      
        {id: 2, value: 'Andy'},
      
        {id: 3, value: 'Jimmy'},
      
        {id: 4, value: 'Alex'},
      
        {id: 0, value: 'John'},
      
        {id: 2, value: 'Andy'},
      
        {id: 3, value: 'Jimmy'},
      
        {id: 4, value: 'Alex'},
      
        {id: 0, value: 'John'},
      
        {id: 2, value: 'Andy'},
      
        {id: 3, value: 'Jimmy'},
      
        {id: 4, value: 'Alex'},
      
        {id: 0, value: 'John'},
      
        {id: 2, value: 'Andy'},
      
        {id: 3, value: 'Jimmy'},
      
        {id: 4, value: 'Alex'},
      
        {id: 0, value: 'John'},
      
        {id: 2, value: 'Andy'},
      
        {id: 3, value: 'Jimmy'},
      
        {id: 4, value: 'Alex'},
      
        {id: 0, value: 'John'},
      
        {id: 2, value: 'Andy'},
      
        {id: 3, value: 'Jimmy'},
      
        {id: 4, value: 'Alex'},
      
        {id: 0, value: 'John'},
      
        {id: 2, value: 'Andy'},
      
        {id: 3, value: 'Jimmy'},
      
        {id: 4, value: 'Alex'},
      
    ]
      

      
    callback(data);
      
}
      

      
function getSurname(id, callback) {
      

      
    console.log(`Querying for lastname id ${id}`)
      

      
    let data = [
      
        'Andersen',
      
        'Johsen',
      
        'Falon',
      
        'Alexander',
      
    ]
      

      
    setTimeout(() => {
      
        callback(data[id]);
      
    }, 2000);
      
}


      Here is the result of the program:



      Program start
      
Returning list of firstnames
      
Querying for lastname id 0
      
Querying for lastname id 2
      
Querying for lastname id 3
      
Querying for lastname id 4
      
Querying for lastname id 0
      
Querying for lastname id 2
      
Querying for lastname id 3
      
Querying for lastname id 4
      
Querying for lastname id 0
      
Querying for lastname id 2
      
Querying for lastname id 3
      
Querying for lastname id 4
      
Querying for lastname id 0
      
Querying for lastname id 2
      
Querying for lastname id 3
      
Querying for lastname id 4
      
Querying for lastname id 0
      
Querying for lastname id 2
      
Querying for lastname id 3
      
Querying for lastname id 4
      
Querying for lastname id 0
      
Querying for lastname id 2
      
Querying for lastname id 3
      
Querying for lastname id 4
      
Querying for lastname id 0
      
Querying for lastname id 2
      
Querying for lastname id 3
      
Querying for lastname id 4
      
Querying for lastname id 0
      
Querying for lastname id 2
      
Querying for lastname id 3
      
Querying for lastname id 4
      
Querying for lastname id 0
      
Querying for lastname id 2
      
Querying for lastname id 3
      
Querying for lastname id 4
      
Querying for lastname id 0
      
Querying for lastname id 2
      
Querying for lastname id 3
      
Querying for lastname id 4
      
John Andersen
      
Andy Falon
      
Jimmy Alexander
      
Alex undefined
      
John Andersen
      
Andy Falon
      
Jimmy Alexander
      
Alex undefined
      
John Andersen
      
Andy Falon
      
Jimmy Alexander
      
Alex undefined
      
John Andersen
      
Andy Falon
      
Jimmy Alexander
      
Alex undefined
      
John Andersen
      
Andy Falon
      
Jimmy Alexander
      
Alex undefined
      
John Andersen
      
Andy Falon
      
Jimmy Alexander
      
Alex undefined
      
John Andersen
      
Andy Falon
      
Jimmy Alexander
      
Alex undefined
      
John Andersen
      
Andy Falon
      
Jimmy Alexander
      
Alex undefined
      
John Andersen
      
Andy Falon
      
Jimmy Alexander
      
Alex undefined
      
John Andersen
      
Andy Falon
      
Jimmy Alexander
      
Alex undefined


      As you can see, there are several records with undefined value. Also I have added a setTimeout to emulate that each rest call takes a few seconds. What happens is that all the queries are fired off instantly, then it goes 2 seconds before all the responses return simultaneous.



      I would expect this to wait for each second rest call and then return the result.



      How can I solve this issue?



      Best regards,
      Christian






      javascript node.js loops foreach callback




      javascript node.js loops foreach callback






      share|improve this question















      share|improve this question













      share|improve this question




      share|improve this question








      edited Nov 13 at 15:06









      mihai

      23.3k73968




      23.3k73968










      asked Nov 12 at 20:21









      chranmat

      294




      294
























          2 Answers
          2






          active

          oldest

          votes


















          3














          The reason you have undefined is because your data array has length of 4 (indices go from 0 to 3) but your id's range from 0 to 4. Which means that when you reference data[4] you get undefined.






          share|improve this answer





















          • Your right. That was actually a typo in the example code, but I have this problem with my real code.
            – chranmat
            Nov 12 at 20:43



















          2














          There is nothing wrong with your callbacks. The data, however is incorrect. See below:



          function getSurname(id, callback) {
          

          
    console.log(`Querying for lastname id ${id}`)
          

          
    let data = [
          
        'Andersen',
          
        'Johsen',
          
        'Falon',
          
        'Alexander',
          
    ]
          

          
    setTimeout(() => {
          
        callback(data[id]);
          
    }, 2000);
          
}


          Everytime Alex is called, you're passing id 4 for use in your data array. Remember that array's are 0 based so data[4] = undefined...






          share|improve this answer





















          • Ref comment on previous answer. I can see I did a typo there and that my example actually works. This does not solve the problem in my real code :(
            – chranmat
            Nov 12 at 20:47










          • @chranmat No worries. Can you post your actual code please?
            – War10ck
            Nov 12 at 20:48










          • pastebin.com/XpcWUtrv
            – chranmat
            Nov 12 at 21:06











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          2 Answers
          2






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          2 Answers
          2






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          3














          The reason you have undefined is because your data array has length of 4 (indices go from 0 to 3) but your id's range from 0 to 4. Which means that when you reference data[4] you get undefined.






          share|improve this answer





















          • Your right. That was actually a typo in the example code, but I have this problem with my real code.
            – chranmat
            Nov 12 at 20:43
















          3














          The reason you have undefined is because your data array has length of 4 (indices go from 0 to 3) but your id's range from 0 to 4. Which means that when you reference data[4] you get undefined.






          share|improve this answer





















          • Your right. That was actually a typo in the example code, but I have this problem with my real code.
            – chranmat
            Nov 12 at 20:43














          3












          3








          3






          The reason you have undefined is because your data array has length of 4 (indices go from 0 to 3) but your id's range from 0 to 4. Which means that when you reference data[4] you get undefined.






          share|improve this answer












          The reason you have undefined is because your data array has length of 4 (indices go from 0 to 3) but your id's range from 0 to 4. Which means that when you reference data[4] you get undefined.







          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered Nov 12 at 20:28









          ODYN-Kon

          2,0841625




          2,0841625












          • Your right. That was actually a typo in the example code, but I have this problem with my real code.
            – chranmat
            Nov 12 at 20:43


















          • Your right. That was actually a typo in the example code, but I have this problem with my real code.
            – chranmat
            Nov 12 at 20:43
















          Your right. That was actually a typo in the example code, but I have this problem with my real code.
          – chranmat
          Nov 12 at 20:43




          Your right. That was actually a typo in the example code, but I have this problem with my real code.
          – chranmat
          Nov 12 at 20:43













          2














          There is nothing wrong with your callbacks. The data, however is incorrect. See below:



          function getSurname(id, callback) {
          

          
    console.log(`Querying for lastname id ${id}`)
          

          
    let data = [
          
        'Andersen',
          
        'Johsen',
          
        'Falon',
          
        'Alexander',
          
    ]
          

          
    setTimeout(() => {
          
        callback(data[id]);
          
    }, 2000);
          
}


          Everytime Alex is called, you're passing id 4 for use in your data array. Remember that array's are 0 based so data[4] = undefined...






          share|improve this answer





















          • Ref comment on previous answer. I can see I did a typo there and that my example actually works. This does not solve the problem in my real code :(
            – chranmat
            Nov 12 at 20:47










          • @chranmat No worries. Can you post your actual code please?
            – War10ck
            Nov 12 at 20:48










          • pastebin.com/XpcWUtrv
            – chranmat
            Nov 12 at 21:06
















          2














          There is nothing wrong with your callbacks. The data, however is incorrect. See below:



          function getSurname(id, callback) {
          

          
    console.log(`Querying for lastname id ${id}`)
          

          
    let data = [
          
        'Andersen',
          
        'Johsen',
          
        'Falon',
          
        'Alexander',
          
    ]
          

          
    setTimeout(() => {
          
        callback(data[id]);
          
    }, 2000);
          
}


          Everytime Alex is called, you're passing id 4 for use in your data array. Remember that array's are 0 based so data[4] = undefined...






          share|improve this answer





















          • Ref comment on previous answer. I can see I did a typo there and that my example actually works. This does not solve the problem in my real code :(
            – chranmat
            Nov 12 at 20:47










          • @chranmat No worries. Can you post your actual code please?
            – War10ck
            Nov 12 at 20:48










          • pastebin.com/XpcWUtrv
            – chranmat
            Nov 12 at 21:06














          2












          2








          2






          There is nothing wrong with your callbacks. The data, however is incorrect. See below:



          function getSurname(id, callback) {
          

          
    console.log(`Querying for lastname id ${id}`)
          

          
    let data = [
          
        'Andersen',
          
        'Johsen',
          
        'Falon',
          
        'Alexander',
          
    ]
          

          
    setTimeout(() => {
          
        callback(data[id]);
          
    }, 2000);
          
}


          Everytime Alex is called, you're passing id 4 for use in your data array. Remember that array's are 0 based so data[4] = undefined...






          share|improve this answer












          There is nothing wrong with your callbacks. The data, however is incorrect. See below:



          function getSurname(id, callback) {
          

          
    console.log(`Querying for lastname id ${id}`)
          

          
    let data = [
          
        'Andersen',
          
        'Johsen',
          
        'Falon',
          
        'Alexander',
          
    ]
          

          
    setTimeout(() => {
          
        callback(data[id]);
          
    }, 2000);
          
}


          Everytime Alex is called, you're passing id 4 for use in your data array. Remember that array's are 0 based so data[4] = undefined...







          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered Nov 12 at 20:28









          War10ck

          10.1k62945




          10.1k62945












          • Ref comment on previous answer. I can see I did a typo there and that my example actually works. This does not solve the problem in my real code :(
            – chranmat
            Nov 12 at 20:47










          • @chranmat No worries. Can you post your actual code please?
            – War10ck
            Nov 12 at 20:48










          • pastebin.com/XpcWUtrv
            – chranmat
            Nov 12 at 21:06


















          • Ref comment on previous answer. I can see I did a typo there and that my example actually works. This does not solve the problem in my real code :(
            – chranmat
            Nov 12 at 20:47










          • @chranmat No worries. Can you post your actual code please?
            – War10ck
            Nov 12 at 20:48










          • pastebin.com/XpcWUtrv
            – chranmat
            Nov 12 at 21:06
















          Ref comment on previous answer. I can see I did a typo there and that my example actually works. This does not solve the problem in my real code :(
          – chranmat
          Nov 12 at 20:47




          Ref comment on previous answer. I can see I did a typo there and that my example actually works. This does not solve the problem in my real code :(
          – chranmat
          Nov 12 at 20:47












          @chranmat No worries. Can you post your actual code please?
          – War10ck
          Nov 12 at 20:48




          @chranmat No worries. Can you post your actual code please?
          – War10ck
          Nov 12 at 20:48












          pastebin.com/XpcWUtrv
          – chranmat
          Nov 12 at 21:06




          pastebin.com/XpcWUtrv
          – chranmat
          Nov 12 at 21:06


















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