Handling optional parameters in javascript

Question

I have a static javascript function that can take 1, 2 or 3 parameters:

function getData(id, parameters, callback) //parameters (associative array) and callb         


        

Answer 1

Are you saying you can have calls like these: getData(id, parameters); getData(id, callback)?

In this case you can't obviously rely on position and you have to rely on analysing the type: getType() and then if necessary getTypeName()

Check if the parameter in question is an array or a function.

Answer 2

I recommend you to use ArgueJS.

You can just type your function this way:

function getData(){
  arguments = __({id: String, parameters: [Object], callback: [Function]})

  // and now access your arguments by arguments.id,
  //          arguments.parameters and arguments.callback
}

I considered by your examples that you want your id parameter to be a string, right? Now, getData is requiring a String id and is accepting the optionals Object parameters and Function callback. All the use cases you posted will work as expected.

Answer 3

I think you want to use typeof() here:

function f(id, parameters, callback) {
  console.log(typeof(parameters)+" "+typeof(callback));
}

f("hi", {"a":"boo"}, f); //prints "object function"
f("hi", f, {"a":"boo"}); //prints "function object"

Answer 4

So use the typeof operator to determine if the second parameter is an Array or function.

This can give some suggestions: http://www.planetpdf.com/developer/article.asp?ContentID=testing_for_object_types_in_ja

I am not certain if this is work or homework, so I don't want to give you the answer at the moment, but the typeof will help you determine it.

Answer 5

You can use the arguments object property inside the function.

Answer 6

If your problem is only with function overloading (you need to check if 'parameters' parameter is 'parameters' and not 'callback'), i would recommend you don't bother about argument type and
use this approach. The idea is simple - use literal objects to combine your parameters:

function getData(id, opt){
    var data = voodooMagic(id, opt.parameters);
    if (opt.callback!=undefined)
      opt.callback.call(data);
    return data;         
}

getData(5, {parameters: "1,2,3", callback: 
    function(){for (i=0;i<=1;i--)alert("FAIL!");}
});