A snippet that wrap a common ajax object provided by jquery-like libraries. I never tested it, just work few minutes. Maybe it work, maybe not.

ajaxPolling.js

  var AjaxPolling = function(url, data, interval, settings){

    //Optionnal parameters filling.
    if(typeof settings === 'undefined'){ settings = {};}
    if(typeof interval === 'undefined'){ interval = null;}

    //Setting Object attributes.
    this.url = url;
    this.settings = $.extend(true,
      {}, settings, AjaxPolling.prototype._defaultSettings
    );
    this.interval = interval;
    if(this.interval !== null){
      this.settings.timeout = this.interval - 1;
    }

    //Launching the request.
    // __/!\ Should never be moved. /!\__
    this.request();

    if(this.interval !== null){
      this._intervalID = window.setInterval(this.request, this.interval);
    }


    return this;
  };

  AjaxPolling.prototype = {

    _defaultSettings : {
      async: true,
      cache: false,
      type : 'GET'
    },

    /**
     * Request asynchronously the server.
     *
     * @return {Object} this
     * @chainable
     */
    request: function(){
      this.jqXHR = $.ajax(this.url, this.settings);
      return this;
    },

    /**
     * Add a `done` callback.
     *
     * @param  {Function} callback [description]
     * @return {Object} this
     * @chainable
     */
    done: function(callback, context){
      context = (typeof context !== 'undefined' ? context : this);
      this.jqXHR.done.call(context, callback);
      return this;
    },

    /**
     * Add a `fail` callback.
     *
     * @param  {Function} callback [description]
     * @return {Object} this
     * @chainable
     */
    fail: function(callback, context){
      context = (typeof context !== 'undefined' ? context : this);
      this.jqXHR.fail.call(context, callback);
      return this;
    },

    /**
     * Add an `always` callback.
     *
     * @param  {Function} callback [description]
     * @return {Object} this
     * @chainable
     */
    always: function(callback, context){
      context = (typeof context !== 'undefined' ? context : this);
      this.jqXHR.always.call(context, callback);
      return this;
    },

    /**
     * Add a `then` callback.
     *
     * @param  {Function} callback [description]
     * @return {Object} this
     * @chainable
     */
    then: function(successCb, failCb, progressCb, context){
      context = (typeof context !== 'undefined' ? context : this);
      this.jqXHR.then.call(context, callback);
      return this;
    },

    kill: function(){
      clearInterval(this._intervalID);
      return this;
    }
  };