Callback: "Object is not a function"

I am trying to use CoffeeScript to setup an AJAX callback function like so:

The Pattern

function doAjax(callback)
{
  $.ajax(url, data)
    .done(function(){
       // ... do stuff here ...
       callback(true);
    }).fail(function(){
       callback(false);
    });
}

function doSomething()
{
  doAjax(function(result){
    if (result == true )
       console.log('success');
    else
       console.log('failed');
  });
}

I am using the following CoffeeScript to do this (this is within an object):

CoffeeScript

doAjax: (callback) ->
  $.getJSON(url)
    .done( (data) ->
      if something == true
        callback(true)
      else
        callback(false)
    ).fail( () ->
      callback(false)
    )

doSomething: () ->
  this.doAjax(function:(result)->
    if result == true
      console.log "true"
    else
      console.log "false"

It results in the following compiled JavaScript like this:

Compiled JS

MyObject.prototype.doAjax = function(callback) {

  return $.getJSON(url).done(function(data) {
    if (something == true) {
      callback(true);  // <--- The error happens here
    } else {
      callback(false);
    }
  }).fail(function() {
    callback(false);
  });
};

MyObject.prototype.doSomething = function() {

  return this.doAjax({
    "function": function(result) {
      var message;

      if (result === true) {

        return console.log("true");
      } else {
        return console.log("false");
      }
    }
  });
};

And I get the error (at the marked line above):

Uncaught TypeError: object is not a function 

What am I doing wrong in my CoffeeScript here?