Function in JavaScript that can be called only once

Question

I need to create a function which can be executed only once  in each time after the first it won t be executed  I know from C   and Java about static variables that can do the work but I would like to know if there is a more elegant way to do this

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You could simply have the function  remove itself    function Once        console log  run         Once   undefined     Once        run Once        Uncaught TypeError  undefined is not a function    But this may not be the best answer if you don t want to be swallowing errors    You could also do this   function Once        console log  run         Once   function         Once       run Once       nothing happens   I need it to work like smart pointer  if there no elements from type A it can be executed  if there is one or more A elements the function can t be executed   function Conditional        if    lt no elements from type A gt   return          do stuff

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Talking about static variables  this is a little bit like closure variant    var once   function         if once done  return      console log  Doing this once         once done   true      once    once       You could then reset a function if you wish    once done   false

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Reusable invalidate function which works with setInterval   var myFunc   function       if  invalidate arguments   return    console log  called once and never again        your stuff here     const invalidate   function a      var fired   a callee fired    a callee fired   true    return fired     setInterval myFunc  1000     Try it on JSBin  https   jsbin com vicipar edit js console  Variation of answer from Bunyk

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JQuery allows to call the function only once using the method one      x000D   x000D  let func   function     x000D    console log  Calling just once     x000D    x000D     x000D  let elem       example    x000D     x000D  elem one  click   func   x000D   lt script src  https   cdnjs cloudflare com ajax libs jquery 3 3 1 jquery min js  gt  lt  script gt  x000D   lt div gt  x000D     lt p gt Function that can be called only once lt  p gt  x000D     lt button id  example   gt JQuery one   lt  button gt  x000D   lt  div gt  x000D   x000D   x000D    Implementation using JQuery method on      x000D   x000D  let func   function e    x000D    console log  Calling just once     x000D      e target  off e type  func  x000D    x000D     x000D  let elem       example    x000D     x000D  elem on  click   func   x000D   lt script src  https   cdnjs cloudflare com ajax libs jquery 3 3 1 jquery min js  gt  lt  script gt  x000D   lt div gt  x000D     lt p gt Function that can be called only once lt  p gt  x000D     lt button id  example   gt JQuery on   lt  button gt  x000D   lt  div gt  x000D   x000D   x000D    Implementation using native JS    x000D   x000D  let func   function e    x000D    console log  Calling just once     x000D    e target removeEventListener e type  func   x000D    x000D     x000D  let elem   document getElementById  example    x000D     x000D  elem addEventListener  click   func   x000D   lt div gt  x000D     lt p gt Functions that can be called only once lt  p gt  x000D     lt button id  example   gt ECMAScript addEventListener lt  button gt  x000D   lt  div gt  x000D   x000D   x000D

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If your using Node js or writing JavaScript with browserify  consider the  once  npm module   var once   require  once    function load  file  cb      cb   once cb    loader load  file     loader once  load   cb    loader once  error   cb

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If you want to be able to reuse the function in the future then this works well based on ed Hopp s code above  I realize that the original question didn t call for this extra feature        var something    function        var executed   false                    return function value               if an argument is not present then         if arguments length    0                               if   executed                executed   true                Do stuff here only once unless reset             console log  Hello World                               else return             else                  otherwise allow the function to fire again             executed   value              return                                something     Hello World  something    something    console log  Reset      Reset something false   something     Hello World  something    something      The output look like   Hello World  Reset Hello World

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UnderscoreJs has a function that does that  underscorejs org  once       Returns a function that will be executed at most one time  no matter how      often you call it  Useful for lazy initialization      once   function func        var ran   false  memo      return function           if  ran  return memo        ran   true        memo   func apply this  arguments         func   null        return memo

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If you re using Ramda  you can use the function  once     A quote from the documentation      once Function     a      b     a      b    PARAMETERS   Added in v0 1 0      Accepts a function fn and returns a function that guards invocation of fn such that fn can only ever be called once  no matter how many times the returned function is invoked  The first value calculated is returned in subsequent invocations    var addOneOnce   R once x   gt  x   1   addOneOnce 10       gt  11 addOneOnce addOneOnce 50        gt  11

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If by  won t be executed  you mean  will do nothing when called more than once   you can create a closure   var something    function         var executed   false      return function             if   executed                executed   true                 do something                         something        do something  happens something       nothing happens   In answer to a comment by  Vladloffe  now deleted   With a global variable  other code could reset the value of the  executed  flag  whatever name you pick for it   With a closure  other code has no way to do that  either accidentally or deliberately   As other answers here point out  several libraries  such as Underscore and Ramda  have a little utility function  typically named once       that accepts a function as an argument and returns another function that calls the supplied function exactly once  regardless of how many times the returned function is called  The returned function also caches the value first returned by the supplied function and returns that on subsequent calls   However  if you aren t using such a third-party library  but still want such a utility function  rather than the nonce solution I offered above   it s easy enough to implement  The nicest version I ve seen is this one posted by David Walsh   function once fn  context         var result      return function              if  fn                result   fn apply context    this  arguments               fn   null                    return result             I would be inclined to change fn   null  to fn   context   null   There s no reason for the closure to maintain a reference to context once fn has been called       Be aware  though  that other libraries  such as this Drupal extension to jQuery  may have a function named once   that does something quite different

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try this   var fun    function       var called   false    return function         if   called          console log  I  called          called   true

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Replace it with a reusable NOOP  no operation  function      this function does nothing function noop        function foo         foo   noop     swap the functions         do your thing    function bar         bar   noop     swap the functions         do your thing

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Here is an example JSFiddle - http   jsfiddle net 6yL6t   And the code   function hashCode str        var hash   0  i  chr  len      if  str length    0  return hash      for  i   0  len   str length  i  lt  len  i              chr     str charCodeAt i           hash      hash  lt  lt  5  - hash    chr          hash    0     Convert to 32bit integer           return hash     var onceHashes        function once func        var unique   hashCode func toString   match  function          s S         1         if   onceHashes unique             onceHashes unique    true          func              You could do   for  var i 0  i lt 10  i          once function             alert i               And it will run only once

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Initial setup   var once   function  once fn         var ret  is called         return new function which is our control function         to make sure once fn is only called once      return function arg1  arg2  arg3            if   is called   return ret          is called   true             return the result from once fn and store to so we can return it multiply times             you might wanna look at Function prototype apply          ret   once fn arg1  arg2  arg3           return ret

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var init   function         console log  logges only once        init   false       if init    init          next time executing init   will cause error because now init is     -equal to false  thus typing init will return false

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This one is useful for preventing infinite loops  using jQuery     lt script gt  var doIt   true  if doIt        do stuff      body   html String    body   html    replace  var doIt   true                                                        var doIt   false          lt  script gt    If you re worried about namespace pollution  subsitute a long  random string for  doIt

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var quit   false   function something         if quit           return             quit   true          other code

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keep it as simple as possible  function sree      console log  hey      window sree      gt         You can see the result

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simple decorator that easy to write when you need   function one func      return function           func  amp  amp  func apply this  arguments        func   null          using   var initializer  one      gt         console log  initializing         initializer       initializing  initializer      nop initializer      nop

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Trying to use underscore  once  function   var initialize     once createApplication   initialize    initialize       Application is only created once    http   underscorejs org  once

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Tossing my hat in the ring for fun  added advantage of memoizing const callOnce    fn  i 0  memo    gt       gt  i     memo    memo   fn         usage const myExpensiveFunction        gt    return console log  joe   5    const memoed   callOnce myExpensiveFunction   memoed      logs  quot joe quot   returns 5 memoed       returns 5 memoed       returns 5

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Point to an empty function once it has been called   x000D   x000D  function myFunc         myFunc   function         kill it as soon as it was called      console log  call once and never again        your stuff here    x000D   lt button onClick myFunc   gt Call myFunc   lt  button gt  x000D   x000D   x000D    Or  like so   x000D   x000D  var myFunc   function func         if  myFunc fired   return       myFunc fired   true       console log  called once and never again        your stuff here        even if referenced  amp   renamed    refToMyfunc   gt     setInterval refToMyfunc  1000      myFunc  x000D   x000D   x000D

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if   window doesThisOnce     function myFunction            do something     window doesThisOnce   true

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From some dude named Crockford        function once func        return function              var f   func          func   null          return f apply              this              arguments

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It helps to prevent sticky execution   var done   false   function doItOnce func     if  done       done   true      func         setTimeout function        done   false      1000

[javascript] Function in JavaScript that can be called only once

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