JavaScript variable number of arguments to function

Question

Is there a way to allow  unlimited  vars for a function in JavaScript   Example   load var1  var2  var3  var4  var5  etc     load var1

User · Answer

Yes  just like this     function load       var var0   arguments 0     var var1   arguments 1      load 1 2

User · Answer

Sure  just use the arguments object   function foo       for  var i   0  i  lt  arguments length  i          console log arguments i

User · Answer

Another option is to pass in your arguments in a context object   function load context           do whatever with context name  context address  etc     and use it like this  load  name  Ken  address  secret  unused true     This has the advantage that you can add as many named arguments as you want  and the function can use them  or not  as it sees fit

User · Answer

In  most  recent browsers  you can accept variable number of arguments with this syntax   function my log    args            args is an Array      console log args           You can pass this array as parameters to another function      console log    args       Here s a small example   function foo x     args      console log x  args     args  arguments      foo  a    b    c   z  d      gt   a Array 3     b    c    d    b c d Arguments      0   a       1   b       2   c       3   d       length  4   Documentation and more examples here  https   developer mozilla org en-US docs Web JavaScript Reference Functions rest parameters

User · Answer

Although I generally agree that the named arguments approach is useful and flexible  unless you care about the order  in which case arguments is easiest   I do have concerns about the cost of the mbeasley approach  using defaults and extends   This is an extreme amount of cost to take for pulling default values  First  the defaults are defined inside the function  so they are repopulated on every call  Second  you can easily read out the named values and set the defaults at the same time using     There is no need to create and merge yet another new object to get this information   function load context       var parameter1   context parameter1    defaultValue1         parameter2   context parameter2    defaultValue2         do stuff     This is roughly the same amount of code  maybe slightly more   but should be a fraction of the runtime cost

User · Answer

As mentioned already  you can use the arguments object to retrieve a variable number of function parameters   If you want to call another function with the same arguments  use apply  You can even add or remove arguments by converting arguments to an array  For example  this function inserts some text before logging to console   log         let args   Array prototype slice call arguments       args     MyObjectName   this id   concat args       console log apply console  args

User · Answer

Use the arguments object when inside the function to have access to all arguments passed in

User · Answer

I agree with Ken s answer as being the most dynamic and I like to take it a step further   If it s a function that you call multiple times with different arguments - I use Ken s design but then add default values   function load context         var defaults             parameter1  defaultValue1          parameter2  defaultValue2                          var context   extend defaults  context           do stuff     This way  if you have many parameters but don t necessarily need to set them with each call to the function  you can simply specify the non-defaults   For the extend method  you can use jQuery s extend method    extend     craft your own or use the following   function extend         for  var i   1  i  lt  arguments length  i            for  var key in arguments i               if  arguments i  hasOwnProperty key                   arguments 0  key    arguments i  key       return arguments 0       This will merge the context object with the defaults and fill in any undefined values in your object with the defaults

User · Answer

Be aware that passing an Object with named properties as Ken suggested adds the cost of allocating and releasing the temporary object to every call  Passing normal arguments by value or reference will generally be the most efficient  For many applications though the performance is not critical but for some it can be

User · Answer

It is preferable to use rest parameter syntax as Ramast pointed out    function  a  b     args       I just want to add some nice property of the    args argument        It is an array  and not an object like arguments  This allows you to apply functions like map or sort directly    It does not include all parameters but only the one passed from it on    E g  function  a  b     args  in this case args contains   argument 3 to arguments length

User · Answer

While  roufamatic did show use of the arguments keyword and  Ken showed a great example of an object for usage I feel neither truly addressed what is going on in this instance and may confuse future readers or instill a bad practice as not explicitly stating a function method is intended to take a variable amount of arguments parameters     function varyArg          return arguments 0    arguments 1       When another developer is looking through your code is it very easy to assume this function does not take parameters  Especially if that developer is not privy to the arguments keyword  Because of this it is a good idea to follow a style guideline and be consistent  I will be using Google s for all examples   Let s explicitly state the same function has variable parameters   function varyArg  var args        return arguments 0    arguments 1       Object parameter VS var args  There may be times when an object is needed as it is the only approved and considered best practice method of an data map  Associative arrays are frowned upon and discouraged   SIDENOTE  The arguments keyword actually returns back an object using numbers as the key  The prototypal inheritance is also the object family  See end of answer for proper array usage in JS  In this case we can explicitly state this also  Note  this naming convention is not provided by Google but is an example of explicit declaration of a param s type  This is important if you are looking to create a more strict typed pattern in your code   function varyArg  args obj        return args obj name     args obj weight    varyArg  name   Brian   weight  150      Which one to choose   This depends on your function s and program s needs  If for instance you are simply looking to return a value base on an iterative process across all arguments passed then most certainly stick with the arguments keyword  If you need definition to your arguments and mapping of the data then the object method is the way to go  Let s look at two examples and then we re done   Arguments usage  function sumOfAll  var args        return arguments reduce function a  b            return a   b         0     sumOfAll 1 2 3      returns 6   Object usage  function myObjArgs args obj           MAKE SURE ARGUMENT IS AN OBJECT OR ELSE RETURN     if  typeof args obj      object             return  Arguments passed must be in object form               return  Hello   args obj name   I see you re   args obj age   years old      myObjArgs  name   Brian   age  31       returns  Hello Brian I see you re 31 years old   Accessing an array instead of an object      args  The rest parameter   As mentioned up top of the answer the arguments keyword actually returns an object  Because of this any method you want to use for an array will have to be called  An example of this   Array prototype map call arguments  function  val  idx  arr         To avoid this use the rest parameter   function varyArgArr     var args        return var args sort      varyArgArr 5 1 3      returns 1  3  5

[javascript] JavaScript variable number of arguments to function

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