How to create a javascript plugin w/ callbacks

plugin.js

function Module(foo, bar) {
  this.foo = foo;
  this.bar = bar;
}

Module.prototype.getData = function(fooFunc) {
  if (!fooFunc || typeof fooFunc !== 'function')
    return;

  if (this.foo == '' || this.bar == '') {
    fooFunc('Fields empty');
  } else {
    fooFunc(null, {foo: this.foo, bar: this.bar});
  }
}

var obj = new Module('it', 'works');
obj.getData(function(err, data) {
  if (err === null) {
    console.log(data);
  } else {
    console.log(err);
  }
});

/*******************
 *******************
 *******************/

Module.prototype.getData = function(fooFunc) {
  if (this.foo == '' || this.bar == '') {
    if (fooFunc && typeof fooFunc.error === 'function')
      fooFunc.error.apply(this, ['No...']);
  } else {
    if (fooFunc && typeof fooFunc.success === 'function')
      fooFunc.success.call(this, 'OKAY, ' + this.foo + ' ' + this.bar + '!');
  }
}

obj.getData({
  success: function(data) {
    alert(data);
  },
  error: function(err) {
    console.log(err);
  }
});