Is it possible to send a variable number of arguments to a JavaScript function

Question

Is it possible to send a variable number of arguments to a JavaScript function  from an array    var arr     a   b   c    var func   function            debug      alert arguments length              for arg in arguments          alert arg      func  a   b   c   d       prints 4 which is what I want  then  a   b   c   d  func arr      prints 1  then  Array    I ve recently written a lot of Python and it s a wonderful pattern to be able to accept varargs and send them  e g   def func  args      print len args     for i in args         print i  func  a   b   c   d       prints 4 which is what I want  then  a   b   c   d  func  arr     prints 4 which is what I want  then  a   b   c   d    Is it possible in JavaScript to send an array to be treated as the arguments array

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It s called the splat operator  You can do it in JavaScript using apply   var arr     a   b   c   d    var func   function            debug      console log arguments length       console log arguments     func  a   b   c   d       prints 4 which is what I want  then  a   b   c   d  func arr      prints 1  then  Array  func apply null  arr

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Do you want your function to react to an array argument or variable arguments  If the latter  try   var func   function    rest      alert rest length         In JS  don t use for  in with arrays      use for  of that consumes array s pre-defined iterator      or a more functional approach   rest forEach  v    gt  console log v         But if you wish to handle an array argument  var fn   function arr      alert arr length      for var i of arr        console log i

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The apply function takes two arguments  the object this will be binded to  and the arguments  represented with an array   some func   function  a  b    return b   some func apply obj    arguments    are    here        are

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Yes you can pass variable no  of arguments to a function  You can use apply to achieve this   E g    var arr     Hi   How   are   you     function applyTest        var arg   arguments length      console log arg      applyTest apply null arr

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Update  Since ES6  you can simply use the spread syntax when calling the function   func    arr     Since ES6 also if you expect to treat your arguments as an array  you can also use the spread syntax in the parameter list  for example   function func    args      args forEach arg   gt  console log arg      const values     a    b    c   func    values  func 1  2  3    And you can combine it with normal parameters  for example if you want to receive the first two arguments separately and the rest as an array   function func first  second     theRest                And maybe is useful to you  that you can know how many arguments a function expects   var test   function  one  two  three       test length    3    But anyway you can pass an arbitrary number of arguments     The spread syntax is shorter and  sweeter  than apply and if you don t need to set the this value in the function call  this is the way to go   Here is an apply example  which was the former way to do it   var arr     a   b   c     function func       console log this       test    console log arguments length      3    for var i   0  i  lt  arguments length  i          console log arguments i             func apply  test   arr     Nowadays I only recommend using apply only if you need to pass an arbitrary number of arguments from an array and set the this value  apply takes is the this value as the first arguments  which will be used on the function invocation  if we use null in non-strict code  the this keyword will refer to the Global object  window  inside func  in strict mode  when explicitly using  use strict  or in ES modules  null will be used   Also note that the arguments object is not really an Array  you can convert it by   var argsArray   Array prototype slice call arguments     And in ES6   const argsArray       arguments     or Array from arguments    But you rarely use the arguments object directly nowadays thanks to the spread syntax

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There are two methods as of ES2015   The arguments Object  This object is built into functions  and it refers to  appropriately  the arguments of a function  It is not technically an array  though  so typical array operations won t work on it  The suggested method is to use Array from or the spread operator to create an array from it   I ve seen other answers mention using slice  Don t do that  It prevents optimizations  source  MDN    Array from arguments      arguments    However  I would argue that arguments is problematic because it hides what a function accepts as input  An arguments function typically is written like this   function mean        let args       arguments       return args reduce  a b   gt a b    args length      Sometimes  the function header is written like the following to document the arguments in a C-like fashion   function mean                     But that is rare   As for why it is problematic  take C  for example  C is backwards compatible with an ancient pre-ANSI dialect of the language known as K amp R C  K amp R C allows function prototypes to have an empty arguments list   int myFunction       This function accepts unspecified parameters      ANSI C provides a facility for varargs        and void to specify an empty arguments-list   int myFunction void      This function accepts no parameters      Many people inadvertently declare functions with an unspecified arguments list  int myfunction      when they expect the function to take zero arguments  This is technically a bug because the function will accept arguments  Any number of them   A proper varargs function in C takes the form   int myFunction int nargs          And JavaScript actually does have something similar to this   Spread Operator   Rest Parameters  I ve already shown you the spread operator  actually      name   It s pretty versatile  and can also be used in a function s argument-list   rest parameters   to specify varargs in a nicely documented fashion   function mean    args       return args reduce  a b   gt a b    args length      Or as a lambda expression        args   gt args reduce  a b   gt a b    args length  1 2 3 4 5      3   I much prefer the spread operator  It is clean and self-documenting

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You can actually pass as many values as you want to any javascript function   The explicitly named parameters will get the first few values  but ALL parameters will be stored in the arguments array   To pass the arguments array in  unpacked  form  you can use apply  like so  c f  Functional Javascript    var otherFunc   function        alert arguments length      Outputs  10    var myFunc   function       alert arguments length      Outputs  10   otherFunc apply this  arguments     myFunc 1 2 3 4 5 6 7 8 9 10

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For those who were redirected here from Passing variable number of arguments from one function to another  which should not be marked as a duplicate of this question    If you re trying to pass a variable number of arguments from one function to another  since JavaScript 1 8 5 you can simply call apply   on the second function and pass in the arguments parameter   var caller   function         callee apply  null  arguments       var callee   function         alert  arguments length       caller   Hello    World    88       Shows  3     Note  The first argument is the this parameter to use  Passing null will call the function from the global context  i e  as a global function instead of the method of some object   According to this document  the ECMAScript 5 specification redefined the apply   method to take any  generic array-like object   instead of strictly an Array  Thus  you can directly pass the arguments list into the second function   Tested in Chrome 28 0  Safari 6 0 5  and IE 10  Try it out with this JSFiddle

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function window      var proxied   window alert    window alert   function         return proxied apply window  arguments          this     alert 13  37

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This is a sample program for calculating sum of integers for variable arguments and array on integers  Hope this helps   var CalculateSum   function        calculateSumService apply  null  arguments       var calculateSumService   function        var sum   0       if  arguments length     1           var args   arguments 0            for var i   0 i lt args length  i                sum    args i                   else          for var i   0 i lt arguments length  i                sum    arguments i                                  alert sum          Sample method call     CalculateSum 10 20 30                CalculateSum  10 20 30 40 50        CalculateSum 10 20

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With ES6 you can use rest parameters for varagrs  This takes the argument list and converts it to an array   function logArgs    args        console log args length      for let arg of args            console log arg

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The splat and spread operators are part of ES6  the planned next version of Javascript  So far only Firefox supports them  This code works in FF16    var arr     quick    brown    lazy     var sprintf   function str     args        for  arg of args            str   str replace   s   arg             return str     sprintf apply null    The  s  s fox jumps over the  s dog       arr    sprintf  The  s  s fox jumps over the  s dog     slow    red    sleeping      Note the awkard syntax for spread  The usual syntax of sprintf  The  s  s fox jumps over the  s dog       arr   is not yet supported  You can find an ES6 compatibility table here   Note also the use of for   of  another ES6 addition  Using for   in for arrays is a bad idea

[javascript] Is it possible to send a variable number of arguments to a JavaScript function?

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