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Why do variable in an inner function return nan when there is the same variable name at the inner function declared after log



The Next CEO of Stack OverflowWhat is the naming convention in Python for variable and function names?How to execute a JavaScript function when I have its name as a stringWhat is a practical use for a closure in JavaScript?Javascript by reference vs. by valueWhy aren't ◎ܫ◎ and ☺ valid JavaScript variable names?What is the explanation for these bizarre JavaScript behaviours mentioned in the 'Wat' talk for CodeMash 2012?Is the recommendation to include CSS before JavaScript invalid?variable not writable in inner functionjavascript variable returning NaNFunction returns NaN when it shouldn't










7















What's happening here? I get a different result if I declare a variable after console.log in the inner function



I understand that var has a functional scope and inner function can access the variable from their parent






function outer() 
var a = 2;

function inner()
a++;
console.log(a) //log NaN
var a = 8

inner()

outer()








function outer() 
var a = 2;

function inner()
a++;
console.log(a) //log 3
var b = 8

inner()

outer()





The log returns NaN in the first example and log 3 in the second example










share|improve this question




























    7















    What's happening here? I get a different result if I declare a variable after console.log in the inner function



    I understand that var has a functional scope and inner function can access the variable from their parent






    function outer() 
    var a = 2;

    function inner()
    a++;
    console.log(a) //log NaN
    var a = 8

    inner()

    outer()








    function outer() 
    var a = 2;

    function inner()
    a++;
    console.log(a) //log 3
    var b = 8

    inner()

    outer()





    The log returns NaN in the first example and log 3 in the second example










    share|improve this question


























      7












      7








      7


      1






      What's happening here? I get a different result if I declare a variable after console.log in the inner function



      I understand that var has a functional scope and inner function can access the variable from their parent






      function outer() 
      var a = 2;

      function inner()
      a++;
      console.log(a) //log NaN
      var a = 8

      inner()

      outer()








      function outer() 
      var a = 2;

      function inner()
      a++;
      console.log(a) //log 3
      var b = 8

      inner()

      outer()





      The log returns NaN in the first example and log 3 in the second example










      share|improve this question
















      What's happening here? I get a different result if I declare a variable after console.log in the inner function



      I understand that var has a functional scope and inner function can access the variable from their parent






      function outer() 
      var a = 2;

      function inner()
      a++;
      console.log(a) //log NaN
      var a = 8

      inner()

      outer()








      function outer() 
      var a = 2;

      function inner()
      a++;
      console.log(a) //log 3
      var b = 8

      inner()

      outer()





      The log returns NaN in the first example and log 3 in the second example






      function outer() 
      var a = 2;

      function inner()
      a++;
      console.log(a) //log NaN
      var a = 8

      inner()

      outer()





      function outer() 
      var a = 2;

      function inner()
      a++;
      console.log(a) //log NaN
      var a = 8

      inner()

      outer()





      function outer() 
      var a = 2;

      function inner()
      a++;
      console.log(a) //log 3
      var b = 8

      inner()

      outer()





      function outer() 
      var a = 2;

      function inner()
      a++;
      console.log(a) //log 3
      var b = 8

      inner()

      outer()






      javascript function






      share|improve this question















      share|improve this question













      share|improve this question




      share|improve this question








      edited 1 hour ago









      Nick Parsons

      10.3k2926




      10.3k2926










      asked 1 hour ago









      ClaudeClaude

      476




      476






















          3 Answers
          3






          active

          oldest

          votes


















          11














          This is due to hoisting



          The declaration of a in the inner function is hoisted to the top of the function, overriding the outer function's a, so a is undefined



          undefined++ returns NaN, hence your result.



          Your code is equivalent to:



          function outer() 
          var a=2;

          function inner()
          var a;
          a++;
          console.log(a); //log NaN
          a = 8;


          inner();


          outer();


          Rewriting your code in this way makes it easy to see what's going on.






          share|improve this answer
































            3














            Because var is hoisted through the function, you're essentially running undefined++ which is NaN. If you remove var a = 8 in inner, the code works as expected:






            function outer() 
            var a = 2;

            function inner()
            a++;
            console.log(a);

            inner();

            outer();








            share|improve this answer






























              -2














              They can’t access the inner function value so we have to defined globally. After globally you can use A value anywhere in the code



              var a=0;
              function outer()
              a=2;
              function inner()
              a=a+1;
              console.log(a)
              a = 8

              inner()

              outer()





              share|improve this answer




















              • 3





                How does this piece of code explains the issue? Can you provide an explanation of the code you have posted?

                – Shidersz
                1 hour ago











              • They can’t access the inner function value so we have to defined globally. After globally you can use A value anywhere in the code

                – Darshit Shah
                1 hour ago











              • While this code may solve the question, including an explanation of how and why this solves the problem would really help to improve the quality of your post, and probably result in more up-votes. Remember that you are answering the question for readers in the future, not just the person asking now. Please edit your answer to add explanations and give an indication of what limitations and assumptions apply. From Review

                – double-beep
                42 mins ago











              Your Answer






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              3 Answers
              3






              active

              oldest

              votes








              3 Answers
              3






              active

              oldest

              votes









              active

              oldest

              votes






              active

              oldest

              votes









              11














              This is due to hoisting



              The declaration of a in the inner function is hoisted to the top of the function, overriding the outer function's a, so a is undefined



              undefined++ returns NaN, hence your result.



              Your code is equivalent to:



              function outer() 
              var a=2;

              function inner()
              var a;
              a++;
              console.log(a); //log NaN
              a = 8;


              inner();


              outer();


              Rewriting your code in this way makes it easy to see what's going on.






              share|improve this answer





























                11














                This is due to hoisting



                The declaration of a in the inner function is hoisted to the top of the function, overriding the outer function's a, so a is undefined



                undefined++ returns NaN, hence your result.



                Your code is equivalent to:



                function outer() 
                var a=2;

                function inner()
                var a;
                a++;
                console.log(a); //log NaN
                a = 8;


                inner();


                outer();


                Rewriting your code in this way makes it easy to see what's going on.






                share|improve this answer



























                  11












                  11








                  11







                  This is due to hoisting



                  The declaration of a in the inner function is hoisted to the top of the function, overriding the outer function's a, so a is undefined



                  undefined++ returns NaN, hence your result.



                  Your code is equivalent to:



                  function outer() 
                  var a=2;

                  function inner()
                  var a;
                  a++;
                  console.log(a); //log NaN
                  a = 8;


                  inner();


                  outer();


                  Rewriting your code in this way makes it easy to see what's going on.






                  share|improve this answer















                  This is due to hoisting



                  The declaration of a in the inner function is hoisted to the top of the function, overriding the outer function's a, so a is undefined



                  undefined++ returns NaN, hence your result.



                  Your code is equivalent to:



                  function outer() 
                  var a=2;

                  function inner()
                  var a;
                  a++;
                  console.log(a); //log NaN
                  a = 8;


                  inner();


                  outer();


                  Rewriting your code in this way makes it easy to see what's going on.







                  share|improve this answer














                  share|improve this answer



                  share|improve this answer








                  edited 1 hour ago









                  Shidersz

                  9,3362933




                  9,3362933










                  answered 1 hour ago









                  jrojro

                  584115




                  584115























                      3














                      Because var is hoisted through the function, you're essentially running undefined++ which is NaN. If you remove var a = 8 in inner, the code works as expected:






                      function outer() 
                      var a = 2;

                      function inner()
                      a++;
                      console.log(a);

                      inner();

                      outer();








                      share|improve this answer



























                        3














                        Because var is hoisted through the function, you're essentially running undefined++ which is NaN. If you remove var a = 8 in inner, the code works as expected:






                        function outer() 
                        var a = 2;

                        function inner()
                        a++;
                        console.log(a);

                        inner();

                        outer();








                        share|improve this answer

























                          3












                          3








                          3







                          Because var is hoisted through the function, you're essentially running undefined++ which is NaN. If you remove var a = 8 in inner, the code works as expected:






                          function outer() 
                          var a = 2;

                          function inner()
                          a++;
                          console.log(a);

                          inner();

                          outer();








                          share|improve this answer













                          Because var is hoisted through the function, you're essentially running undefined++ which is NaN. If you remove var a = 8 in inner, the code works as expected:






                          function outer() 
                          var a = 2;

                          function inner()
                          a++;
                          console.log(a);

                          inner();

                          outer();








                          function outer() 
                          var a = 2;

                          function inner()
                          a++;
                          console.log(a);

                          inner();

                          outer();





                          function outer() 
                          var a = 2;

                          function inner()
                          a++;
                          console.log(a);

                          inner();

                          outer();






                          share|improve this answer












                          share|improve this answer



                          share|improve this answer










                          answered 1 hour ago









                          Jack BashfordJack Bashford

                          13.8k31848




                          13.8k31848





















                              -2














                              They can’t access the inner function value so we have to defined globally. After globally you can use A value anywhere in the code



                              var a=0;
                              function outer()
                              a=2;
                              function inner()
                              a=a+1;
                              console.log(a)
                              a = 8

                              inner()

                              outer()





                              share|improve this answer




















                              • 3





                                How does this piece of code explains the issue? Can you provide an explanation of the code you have posted?

                                – Shidersz
                                1 hour ago











                              • They can’t access the inner function value so we have to defined globally. After globally you can use A value anywhere in the code

                                – Darshit Shah
                                1 hour ago











                              • While this code may solve the question, including an explanation of how and why this solves the problem would really help to improve the quality of your post, and probably result in more up-votes. Remember that you are answering the question for readers in the future, not just the person asking now. Please edit your answer to add explanations and give an indication of what limitations and assumptions apply. From Review

                                – double-beep
                                42 mins ago















                              -2














                              They can’t access the inner function value so we have to defined globally. After globally you can use A value anywhere in the code



                              var a=0;
                              function outer()
                              a=2;
                              function inner()
                              a=a+1;
                              console.log(a)
                              a = 8

                              inner()

                              outer()





                              share|improve this answer




















                              • 3





                                How does this piece of code explains the issue? Can you provide an explanation of the code you have posted?

                                – Shidersz
                                1 hour ago











                              • They can’t access the inner function value so we have to defined globally. After globally you can use A value anywhere in the code

                                – Darshit Shah
                                1 hour ago











                              • While this code may solve the question, including an explanation of how and why this solves the problem would really help to improve the quality of your post, and probably result in more up-votes. Remember that you are answering the question for readers in the future, not just the person asking now. Please edit your answer to add explanations and give an indication of what limitations and assumptions apply. From Review

                                – double-beep
                                42 mins ago













                              -2












                              -2








                              -2







                              They can’t access the inner function value so we have to defined globally. After globally you can use A value anywhere in the code



                              var a=0;
                              function outer()
                              a=2;
                              function inner()
                              a=a+1;
                              console.log(a)
                              a = 8

                              inner()

                              outer()





                              share|improve this answer















                              They can’t access the inner function value so we have to defined globally. After globally you can use A value anywhere in the code



                              var a=0;
                              function outer()
                              a=2;
                              function inner()
                              a=a+1;
                              console.log(a)
                              a = 8

                              inner()

                              outer()






                              share|improve this answer














                              share|improve this answer



                              share|improve this answer








                              edited 39 mins ago

























                              answered 1 hour ago









                              Darshit ShahDarshit Shah

                              33




                              33







                              • 3





                                How does this piece of code explains the issue? Can you provide an explanation of the code you have posted?

                                – Shidersz
                                1 hour ago











                              • They can’t access the inner function value so we have to defined globally. After globally you can use A value anywhere in the code

                                – Darshit Shah
                                1 hour ago











                              • While this code may solve the question, including an explanation of how and why this solves the problem would really help to improve the quality of your post, and probably result in more up-votes. Remember that you are answering the question for readers in the future, not just the person asking now. Please edit your answer to add explanations and give an indication of what limitations and assumptions apply. From Review

                                – double-beep
                                42 mins ago












                              • 3





                                How does this piece of code explains the issue? Can you provide an explanation of the code you have posted?

                                – Shidersz
                                1 hour ago











                              • They can’t access the inner function value so we have to defined globally. After globally you can use A value anywhere in the code

                                – Darshit Shah
                                1 hour ago











                              • While this code may solve the question, including an explanation of how and why this solves the problem would really help to improve the quality of your post, and probably result in more up-votes. Remember that you are answering the question for readers in the future, not just the person asking now. Please edit your answer to add explanations and give an indication of what limitations and assumptions apply. From Review

                                – double-beep
                                42 mins ago







                              3




                              3





                              How does this piece of code explains the issue? Can you provide an explanation of the code you have posted?

                              – Shidersz
                              1 hour ago





                              How does this piece of code explains the issue? Can you provide an explanation of the code you have posted?

                              – Shidersz
                              1 hour ago













                              They can’t access the inner function value so we have to defined globally. After globally you can use A value anywhere in the code

                              – Darshit Shah
                              1 hour ago





                              They can’t access the inner function value so we have to defined globally. After globally you can use A value anywhere in the code

                              – Darshit Shah
                              1 hour ago













                              While this code may solve the question, including an explanation of how and why this solves the problem would really help to improve the quality of your post, and probably result in more up-votes. Remember that you are answering the question for readers in the future, not just the person asking now. Please edit your answer to add explanations and give an indication of what limitations and assumptions apply. From Review

                              – double-beep
                              42 mins ago





                              While this code may solve the question, including an explanation of how and why this solves the problem would really help to improve the quality of your post, and probably result in more up-votes. Remember that you are answering the question for readers in the future, not just the person asking now. Please edit your answer to add explanations and give an indication of what limitations and assumptions apply. From Review

                              – double-beep
                              42 mins ago

















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