Javascript function argument handling

Question

It seems the best way to deal with arguments in javascript functions is to require the caller to pass an associative array:

example = function(options) {
  alert('option1: ' + options.a + ', option2: ' + options.b);
}

Now arguments are named and not needed in any particular order when calling this function:

example({'b':'hello option2', 'a':'hello option1'});

The only thing I don't like is I have to have all this extra code to deal with required and default arguments, not to mention not allowing extra arguments so the caller knows they called the function wrong:

example = function(options) {
var required_args = ['a', 'd'];
var default_args = {'b':'option2', 'c':'option3'};
var allowed_args = ['a', 'b', 'c', 'd'];
// check required args
// check allowed args
for (var arg in default_args) {
    if (typeof options[arg] == "undefined")
              options[arg] = default_args[arg];
  }
  alert('option1: ' + options.a + ', option2: ' + options.b);
}

Is there a standard way to deal with this? I guess I can create a function like:

deal_with_args(options, required_args, default_args, allowed_args)

And throw some exception if required_args or allowed_args is violated...

Answer 1

1. Why do you want to have arguments in an arbitrary order? This is just confusing for people reading your code
2. A function shouldn't have a lot of arguments - it's a hint that it is doing too much
3. The usual pattern for 'required' and 'default' params doesn't seem so bad to me.

The 'standard' form is something like:

function myFunc(required_param, some_param, param_with_default) {
  // obviously this needs modifiction (ie use 'typeof' as you did) 
  // if you're dealing potentially 'falsey' values
  param_with_default = param_with_default || 'some default value';
  // same caution applies here
  if(!required_param) {
    // throw some exception here, or return an error code, or whatever
  }

  // function code
}

Answer 2

Could you do null coalescing for the required args?

alert('option1: ' + (options.a || default_args[a]) + ', option2: ' + (options.b || default_args[b]));

(Edited to correct the operator error)