gistfile1.js

$.Twitter = function (options) {
  var options = $.extend({ 
    username: '',
    success: function () { }
  }, options);

  if (options.username == '')
    return false;

  $.event.trigger ('twitter_loading');
  var url = 'http://twitter.com/status/user_timeline/'+options.username+'.json?callback=?';
  $.ajax ({
      url: url,
      type: 'get',
      dataType: 'json',
      success: function(data) {
        if (options.success) options.success.apply( this, arguments ); 
        $.event.trigger ('twitter_ready');
      },
  });
}

$.Twitter({
  username: 'username',
  success: function(data) { 
    // do sth with data 
  });