Why does the setInterval callback execute only once?












61















I have this counter I made but I want it to run forever, it's really simple, what am I doing wrong here?



function timer() {

  console.log("timer!")

}



window.setInterval(timer(), 1000)





javascript callback setinterval







share|improve this question




















  • 7





    The problem is timer() invokes the function-object that resulted from evaluating timer and then passes the result (undefined) to setTimeout. So, don't invoke it. Instead, just pass the function-object: setInterval(timer, 1000)

    – user166390
    Apr 16 '12 at 22:57


















61















I have this counter I made but I want it to run forever, it's really simple, what am I doing wrong here?



function timer() {

  console.log("timer!")

}



window.setInterval(timer(), 1000)





javascript callback setinterval







share|improve this question




















  • 7





    The problem is timer() invokes the function-object that resulted from evaluating timer and then passes the result (undefined) to setTimeout. So, don't invoke it. Instead, just pass the function-object: setInterval(timer, 1000)

    – user166390
    Apr 16 '12 at 22:57
















61












61








61


11






I have this counter I made but I want it to run forever, it's really simple, what am I doing wrong here?



function timer() {

  console.log("timer!")

}



window.setInterval(timer(), 1000)





javascript callback setinterval







share|improve this question
















I have this counter I made but I want it to run forever, it's really simple, what am I doing wrong here?



function timer() {

  console.log("timer!")

}



window.setInterval(timer(), 1000)





javascript callback setinterval




javascript callback setinterval






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited Jun 9 '18 at 11:52









Ivar

2,871113140




2,871113140










asked Apr 16 '12 at 22:39









computer_smilecomputer_smile

72011534




72011534








  • 7





    The problem is timer() invokes the function-object that resulted from evaluating timer and then passes the result (undefined) to setTimeout. So, don't invoke it. Instead, just pass the function-object: setInterval(timer, 1000)

    – user166390
    Apr 16 '12 at 22:57
















  • 7





    The problem is timer() invokes the function-object that resulted from evaluating timer and then passes the result (undefined) to setTimeout. So, don't invoke it. Instead, just pass the function-object: setInterval(timer, 1000)

    – user166390
    Apr 16 '12 at 22:57










7




7





The problem is timer() invokes the function-object that resulted from evaluating timer and then passes the result (undefined) to setTimeout. So, don't invoke it. Instead, just pass the function-object: setInterval(timer, 1000)

– user166390
Apr 16 '12 at 22:57







The problem is timer() invokes the function-object that resulted from evaluating timer and then passes the result (undefined) to setTimeout. So, don't invoke it. Instead, just pass the function-object: setInterval(timer, 1000)

– user166390
Apr 16 '12 at 22:57














2 Answers
2






active

oldest

votes


















96














You used a function call instead of a function reference as the first parameter of the setInterval. Do it like this: 



function timer() {

  console.log("timer!");

}



window.setInterval(timer, 1000);


Or shorter (but when the function gets bigger also less readable):



window.setInterval( function() {

  console.log("timer!");

}, 1000)





share|improve this answer





















  • 2





    the answer correctly points out that the callback function should not have the "()" in the argument.

    – Kristian
    Apr 16 '12 at 22:42








  • 2





    According to developer.mozilla.org/en/Extensions/…, the shorter version may cause memory leak.

    – Crend King
    Apr 16 '12 at 22:46






  • 2





    @CrendKing Both versions have the exact same "issue" (also, that is for extensions and does not affect normal webpages/JS) as it is object lifetime that matters.

    – user166390
    Apr 16 '12 at 23:14













  • That's why I said "may", since OP does not specify his use case. Just pay attention if it is extracted from an Mozilla extension.

    – Crend King
    Apr 16 '12 at 23:32













  • How can we change the interval value, for e.g. I have array[10, 5, 2] and want to call timer() based on the interval defined in array. Thanks!

    – OverrockSTAR
    Mar 9 '17 at 15:46



















9














setInterval and setTimeout must be used with callbacks, like:



setInterval(timer, 1000);


or unnamed functions:



setInterval( function() { console.log("timer!"); }, 1000 );


Why your code is not working - when you pass a function as argument to another function with brackets e.g. doSomething ( someFunc() ) you are passing the result of the function.



When the function is passed as object e.g. doSomething ( someFunc ) you are passing a callback. This way someFunc is passed as reference and it is executed somewhere in the calling function. This is the same as the pointers to functions in other languages.



A common mistake is to use the these two functions as shown at w3schools. This makes an implicit call to eval.






share|improve this answer























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    2 Answers
    2






    active

    oldest

    votes








    2 Answers
    2






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    96














    You used a function call instead of a function reference as the first parameter of the setInterval. Do it like this: 



    function timer() {
    
  console.log("timer!");
    
}
    

    
window.setInterval(timer, 1000);


    Or shorter (but when the function gets bigger also less readable):



    window.setInterval( function() {
    
  console.log("timer!");
    
}, 1000)





    share|improve this answer





















    • 2





      the answer correctly points out that the callback function should not have the "()" in the argument.

      – Kristian
      Apr 16 '12 at 22:42








    • 2





      According to developer.mozilla.org/en/Extensions/…, the shorter version may cause memory leak.

      – Crend King
      Apr 16 '12 at 22:46






    • 2





      @CrendKing Both versions have the exact same "issue" (also, that is for extensions and does not affect normal webpages/JS) as it is object lifetime that matters.

      – user166390
      Apr 16 '12 at 23:14













    • That's why I said "may", since OP does not specify his use case. Just pay attention if it is extracted from an Mozilla extension.

      – Crend King
      Apr 16 '12 at 23:32













    • How can we change the interval value, for e.g. I have array[10, 5, 2] and want to call timer() based on the interval defined in array. Thanks!

      – OverrockSTAR
      Mar 9 '17 at 15:46
















    96














    You used a function call instead of a function reference as the first parameter of the setInterval. Do it like this: 



    function timer() {
    
  console.log("timer!");
    
}
    

    
window.setInterval(timer, 1000);


    Or shorter (but when the function gets bigger also less readable):



    window.setInterval( function() {
    
  console.log("timer!");
    
}, 1000)





    share|improve this answer





















    • 2





      the answer correctly points out that the callback function should not have the "()" in the argument.

      – Kristian
      Apr 16 '12 at 22:42








    • 2





      According to developer.mozilla.org/en/Extensions/…, the shorter version may cause memory leak.

      – Crend King
      Apr 16 '12 at 22:46






    • 2





      @CrendKing Both versions have the exact same "issue" (also, that is for extensions and does not affect normal webpages/JS) as it is object lifetime that matters.

      – user166390
      Apr 16 '12 at 23:14













    • That's why I said "may", since OP does not specify his use case. Just pay attention if it is extracted from an Mozilla extension.

      – Crend King
      Apr 16 '12 at 23:32













    • How can we change the interval value, for e.g. I have array[10, 5, 2] and want to call timer() based on the interval defined in array. Thanks!

      – OverrockSTAR
      Mar 9 '17 at 15:46














    96












    96








    96







    You used a function call instead of a function reference as the first parameter of the setInterval. Do it like this: 



    function timer() {
    
  console.log("timer!");
    
}
    

    
window.setInterval(timer, 1000);


    Or shorter (but when the function gets bigger also less readable):



    window.setInterval( function() {
    
  console.log("timer!");
    
}, 1000)





    share|improve this answer















    You used a function call instead of a function reference as the first parameter of the setInterval. Do it like this: 



    function timer() {
    
  console.log("timer!");
    
}
    

    
window.setInterval(timer, 1000);


    Or shorter (but when the function gets bigger also less readable):



    window.setInterval( function() {
    
  console.log("timer!");
    
}, 1000)






    share|improve this answer














    share|improve this answer



    share|improve this answer








    edited Apr 16 '12 at 23:17

























    answered Apr 16 '12 at 22:40









    Koen PetersKoen Peters

    11k52949




    11k52949








    • 2





      the answer correctly points out that the callback function should not have the "()" in the argument.

      – Kristian
      Apr 16 '12 at 22:42








    • 2





      According to developer.mozilla.org/en/Extensions/…, the shorter version may cause memory leak.

      – Crend King
      Apr 16 '12 at 22:46






    • 2





      @CrendKing Both versions have the exact same "issue" (also, that is for extensions and does not affect normal webpages/JS) as it is object lifetime that matters.

      – user166390
      Apr 16 '12 at 23:14













    • That's why I said "may", since OP does not specify his use case. Just pay attention if it is extracted from an Mozilla extension.

      – Crend King
      Apr 16 '12 at 23:32













    • How can we change the interval value, for e.g. I have array[10, 5, 2] and want to call timer() based on the interval defined in array. Thanks!

      – OverrockSTAR
      Mar 9 '17 at 15:46














    • 2





      the answer correctly points out that the callback function should not have the "()" in the argument.

      – Kristian
      Apr 16 '12 at 22:42








    • 2





      According to developer.mozilla.org/en/Extensions/…, the shorter version may cause memory leak.

      – Crend King
      Apr 16 '12 at 22:46






    • 2





      @CrendKing Both versions have the exact same "issue" (also, that is for extensions and does not affect normal webpages/JS) as it is object lifetime that matters.

      – user166390
      Apr 16 '12 at 23:14













    • That's why I said "may", since OP does not specify his use case. Just pay attention if it is extracted from an Mozilla extension.

      – Crend King
      Apr 16 '12 at 23:32













    • How can we change the interval value, for e.g. I have array[10, 5, 2] and want to call timer() based on the interval defined in array. Thanks!

      – OverrockSTAR
      Mar 9 '17 at 15:46








    2




    2





    the answer correctly points out that the callback function should not have the "()" in the argument.

    – Kristian
    Apr 16 '12 at 22:42







    the answer correctly points out that the callback function should not have the "()" in the argument.

    – Kristian
    Apr 16 '12 at 22:42






    2




    2





    According to developer.mozilla.org/en/Extensions/…, the shorter version may cause memory leak.

    – Crend King
    Apr 16 '12 at 22:46





    According to developer.mozilla.org/en/Extensions/…, the shorter version may cause memory leak.

    – Crend King
    Apr 16 '12 at 22:46




    2




    2





    @CrendKing Both versions have the exact same "issue" (also, that is for extensions and does not affect normal webpages/JS) as it is object lifetime that matters.

    – user166390
    Apr 16 '12 at 23:14







    @CrendKing Both versions have the exact same "issue" (also, that is for extensions and does not affect normal webpages/JS) as it is object lifetime that matters.

    – user166390
    Apr 16 '12 at 23:14















    That's why I said "may", since OP does not specify his use case. Just pay attention if it is extracted from an Mozilla extension.

    – Crend King
    Apr 16 '12 at 23:32







    That's why I said "may", since OP does not specify his use case. Just pay attention if it is extracted from an Mozilla extension.

    – Crend King
    Apr 16 '12 at 23:32















    How can we change the interval value, for e.g. I have array[10, 5, 2] and want to call timer() based on the interval defined in array. Thanks!

    – OverrockSTAR
    Mar 9 '17 at 15:46





    How can we change the interval value, for e.g. I have array[10, 5, 2] and want to call timer() based on the interval defined in array. Thanks!

    – OverrockSTAR
    Mar 9 '17 at 15:46













    9














    setInterval and setTimeout must be used with callbacks, like:



    setInterval(timer, 1000);


    or unnamed functions:



    setInterval( function() { console.log("timer!"); }, 1000 );


    Why your code is not working - when you pass a function as argument to another function with brackets e.g. doSomething ( someFunc() ) you are passing the result of the function.



    When the function is passed as object e.g. doSomething ( someFunc ) you are passing a callback. This way someFunc is passed as reference and it is executed somewhere in the calling function. This is the same as the pointers to functions in other languages.



    A common mistake is to use the these two functions as shown at w3schools. This makes an implicit call to eval.






    share|improve this answer




























      9














      setInterval and setTimeout must be used with callbacks, like:



      setInterval(timer, 1000);


      or unnamed functions:



      setInterval( function() { console.log("timer!"); }, 1000 );


      Why your code is not working - when you pass a function as argument to another function with brackets e.g. doSomething ( someFunc() ) you are passing the result of the function.



      When the function is passed as object e.g. doSomething ( someFunc ) you are passing a callback. This way someFunc is passed as reference and it is executed somewhere in the calling function. This is the same as the pointers to functions in other languages.



      A common mistake is to use the these two functions as shown at w3schools. This makes an implicit call to eval.






      share|improve this answer


























        9












        9








        9







        setInterval and setTimeout must be used with callbacks, like:



        setInterval(timer, 1000);


        or unnamed functions:



        setInterval( function() { console.log("timer!"); }, 1000 );


        Why your code is not working - when you pass a function as argument to another function with brackets e.g. doSomething ( someFunc() ) you are passing the result of the function.



        When the function is passed as object e.g. doSomething ( someFunc ) you are passing a callback. This way someFunc is passed as reference and it is executed somewhere in the calling function. This is the same as the pointers to functions in other languages.



        A common mistake is to use the these two functions as shown at w3schools. This makes an implicit call to eval.






        share|improve this answer













        setInterval and setTimeout must be used with callbacks, like:



        setInterval(timer, 1000);


        or unnamed functions:



        setInterval( function() { console.log("timer!"); }, 1000 );


        Why your code is not working - when you pass a function as argument to another function with brackets e.g. doSomething ( someFunc() ) you are passing the result of the function.



        When the function is passed as object e.g. doSomething ( someFunc ) you are passing a callback. This way someFunc is passed as reference and it is executed somewhere in the calling function. This is the same as the pointers to functions in other languages.



        A common mistake is to use the these two functions as shown at w3schools. This makes an implicit call to eval.







        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered Apr 17 '12 at 12:52









        BakudanBakudan

        13.7k84265




        13.7k84265






























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