Calling a javascript function recursively

Question

I can create a recursive function in a variable like so      Count down to 0 recursively      var functionHolder   function  counter        output counter       if  counter  gt  0            functionHolder counter-1             With this  functionHolder 3   would output 3 2 1 0  Let s say I did the following   var copyFunction   functionHolder    copyFunction 3   would output 3 2 1 0 as above  If I then changed functionHolder as follows   functionHolder   function whatever        output  Stop counting       Then functionHolder 3   would give Stop counting   as expected   copyFunction 3   now gives 3 Stop counting  as it refers to functionHolder  not the function  which it itself points to   This could be desirable in some circumstances  but is there a way to write the function so that it calls itself rather than the variable that holds it   That is  is it possible to change only the line functionHolder counter-1   so that going through all these steps still gives 3 2 1 0 when we call copyFunction 3    I tried this counter-1   but that gives me the error this is not a function

User · Answer

You can access the function itself using arguments callee  MDN    if  counter gt 0        arguments callee counter-1       This will break in strict mode  however

User · Answer

Here s one very simple example  var counter   0   function getSlug tokens        var slug            if    tokens length            slug   tokens shift            slug   slug toLowerCase            slug    getSlug tokens            counter    1          console log  THE SLUG ELEMENT IS   s  counter is   s   slug  counter              return slug     var mySlug   getSlug   This    Is    My    Slug     console log  THE SLUG IS   s   mySlug    Notice that the counter counts  quot backwards quot  in regards to what slug s value is  This is because of the position at which we are logging these values  as the function recurs before logging -- so  we essentially keep nesting deeper and deeper into the call-stack before logging takes place  Once the recursion meets the final call-stack item  it trampolines  quot out quot  of the function calls  whereas  the first increment of counter occurs inside of the last nested call  I know this is not a  quot fix quot  on the Questioner s code  but given the title I thought I d generically exemplify Recursion for a better understanding of recursion  outright

User · Answer

I know this is an old question  but I thought I d present one more solution that could be used if you d like to avoid using named function expressions   Not saying you should or should not avoid them  just presenting another solution     var fn    function         var innerFn   function counter          console log counter          if counter  gt  0            innerFn counter-1                       return innerFn             console log  running fn      fn 3      var copyFn   fn     console log  running copyFn      copyFn 3      fn   function     console log  done          console log  fn after reassignment      fn 3      console log  copyFn after reassignment of fn      copyFn 3

User · Answer

You can use the Y-combinator   Wikipedia      ES5 syntax var Y   function Y a      return  function  a        return a a        function  b        return a function  a          return b b  a                        ES6 syntax const Y   a  gt  a  gt a a   b  gt a a  gt b b  a         If the function accepts more than one parameter  const Y   a  gt  a  gt a a   b  gt a     a   gt b b     a       And you can use it as this      ES5 var fn   Y function fn      return function counter        console log counter       if  counter  gt  0          fn counter - 1                     ES6 const fn   Y fn   gt  counter   gt      console log counter     if  counter  gt  0        fn counter - 1

User · Answer

Using Named Function Expressions   You can give a function expression a name that is actually private and is only visible from inside of the function ifself   var factorial   function myself  n        if  n  lt   1            return 1            return n   myself n-1     typeof myself      undefined    Here myself is visible only inside of the function itself   You can use this private name to call the function recursively   See 13  Function Definition of the ECMAScript 5 spec      The Identifier in a FunctionExpression can be referenced from inside the FunctionExpression s FunctionBody to allow the function to call itself recursively  However  unlike in a FunctionDeclaration  the Identifier in a FunctionExpression cannot be referenced from and does not affect the scope enclosing the FunctionExpression    Please note that Internet Explorer up to version 8 doesn t behave correctly as the name is actually visible in the enclosing variable environment  and it references a duplicate of the actual function  see patrick dw s comment below    Using arguments callee   Alternatively you could use arguments callee to refer to the current function   var factorial   function  n        if  n  lt   1            return 1            return n   arguments callee n-1       The 5th edition of ECMAScript forbids use of arguments callee   in strict mode  however       From MDN   In normal code arguments callee refers to the enclosing function  This use case is weak  simply name the enclosing function  Moreover  arguments callee substantially hinders optimizations like inlining functions  because it must be made possible to provide a reference to the un-inlined function if arguments callee is accessed  arguments callee for strict mode functions is a non-deletable property which throws when set or retrieved

[javascript] Calling a javascript function recursively

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