Question

I am a little bit confused by the jQuery documentation. I am looking at this page describing $.getJSON. The code sample is:

$.getJSON('ajax/test.json', function(data) {
  var items = [];

  $.each(data, function(key, val) {
    items.push('<li id="' + key + '">' + val + '</li>');
  });

  $('<ul/>', {
    'class': 'my-new-list',
    html: items.join('')
  }).appendTo('body');
});

But the method signature is jQuery.getJSON( url [, data ] [, success(data, textStatus, jqXHR) ] ), where data is an object sent to the server, and success is a method called when the JSON request returns successfully.

So why does the example code work? It seems to have skipped the second argument. I would have expected the correct code to be:

$.getJSON('ajax/test.json', {}, function(data) {
// and then the same from here

I know that the square brackets mean that the [, data] and [, success] arguments are optional, but I guess I don’t understand how javascript deals with a variable number of arguments.

Thank you for your time.

Answer 1

Inside the jQuery source code :

// shift arguments if data argument was omitted
        if ( jQuery.isFunction( data ) ) {
            type = type || callback;
            callback = data;
            data = undefined;
        }

So it works