code: function(eventType, callback, context) {
        if (isFunction(callback)) {
          context = context || this;
          if (!this._events[eventType]) this._events[eventType] = [];
  
          // normal callback not called.
          var self = this;
          this._events[eventType].push([callback, context, function() {
            self.off(eventType, callback, context);
            callback.apply(this, arguments);
          }]);
        }
        return this;
      }
docs: Attach an event listener to this APICall object.
  @param {string|number} eventType The event to listen to. Can be an http code as number or string,
  success, meta, result, error.
  @param {function} callback Callback to call upon event trigger.
  @param {object} context Context to call the callback in.
  @return {APICall} The current APICall object