The closest idiom for *args would be

function func (a, b /*, *args*/) {

    var star_args = Array.prototype.slice.call (arguments, func.length);

    /* now star_args[0] is the first undeclared argument */

}

taking advantage of the fact that Function.length is the number of arguments given in the function definition.

You could package this up in a little helper routine like

function get_star_args (func, args) {

    return Array.prototype.slice.call (args, func.length);

}

and then do

function func (a, b /*, *args*/) {

    var star_args = get_star_args (func, arguments);

    /* now star_args[0] is the first undeclared argument */

}

If you're in the mood for syntactic sugar, write a function which transforms one function into another one which is called with required and optional arguments, and passes the required arguments along, with any additional optional arguments as an array in final position:

function argsify(fn){

    return function(){

        var args_in   = Array.prototype.slice.call (arguments); //args called with

        var required  = args_in.slice (0,fn.length-1);     //take first n   

        var optional  = args_in.slice (fn.length-1);       //take remaining optional

        var args_out  = required;                          //args to call with

        args_out.push (optional);                          //with optionals as array

        return fn.apply (0, args_out);

    };

}

Use this as follows:

// original function

function myfunc (a, b, star_args) {

     console.log (a, b, star_args[0]); // will display 1, 2, 3

}



// argsify it

var argsified_myfunc = argsify (myfunc);



// call argsified function

argsified_myfunc (1, 2, 3);

Then again, you could just skip all this mumbo jumbo if you are willing to ask the caller to pass the optional arguments as an array to start with:

myfunc (1, 2, [3]);

There is really no analogous solution for **kwargs, since JS has no keyword arguments. Instead, just ask the caller to pass the optional arguments in as an object:

function myfunc (a, b, starstar_kwargs) {

    console.log (a, b, starstar_kwargs.x);

}



myfunc (1, 2, {x:3});

ES6 Update

For completeness, let me add that ES6 solves this problem with the rest parameter feature. See Javascript - '...' meaning