Is there anything can be improved in this JavaScript module?

I really like this code.

Still, 2 observations:

• The code is awfully optimistic, no default error handling ?
• success gets data, textStatus, and jqXHR. I would pass all 3 to the callback function.

Very nice. I like to see some require.js around here.

• As konijn said, you shouldn't be only passing data to the callback. In fact, you don't need an extra function here at all.

  $.ajax({
      [...]
      success: callback
  });
  

• Since getData and postData are not used anywhere else and are public I would just include them in the return statement.

    return {
      getData: function (url, dataType, data, callback) {
         callApi(url, 'GET', dataType, data, callback);
      },
      postData: function (url, data, callback) {
         callApi(url, 'POST', 'json', data, callback)
      }
    };
  

You're passing in a lot of parameters to all of these functions. This might present a usability issue as the developer who uses the functions has to remember the order in which to pass the parameters.

It might be easier to use if the functions accepted a single object parameter:

var callApi = function (options) {
    $.ajax({
        url: options.url,
        type: options.type,
        data: options.data,
        dataType: options.dataType,
        contentType: "application/json",
        success: function (data) {
            options.callback(data);
        }
    });
};

var getData = function (options) {
    options.type = 'GET';
    callApi(options);
};

var postData = function (options) {
    options.type = 'POST';
    options.dataType = 'json';
    callApi(options);
};

And then you'd call your functions like:

var options = {
    url: 'http://api.example.com/post.svc',
    data: { "id": 34021 },
    callback: success
};
dataservice.postData(options);

This also means that if the developer misses a variable, you can fall back to default options in the public facing functions without breaking the order in which parameters are passed.

var postData = function (options) {
    options.type = 'POST';
    options.dataType = 'json';

    if (!options.callback) {
        options.callback = genericSuccess;
    }

    callApi(options);
};