code: function ( obj, event, fn, id, scope, st ) {
  		var uuid = id || utility.genId();
  
  		scope = scope || obj;
  		st    = st    || state.getCurrent();
  
  		if ( obj === undefined || event === null || event === undefined || typeof fn !== "function" ) {
  			throw new Error( label.error.invalidArguments );
  		}
  
  		observer.add( obj, event, function () {
  			fn.apply( scope, arguments );
  			observer.remove( obj, event, uuid, st );
  		}, uuid, scope, st);
  
  		return obj;
  	}
docs: Adds a listener for a single execution
  
  @method once
  @param  {Mixed}    obj   Primitive
  @param  {String}   event Event being fired
  @param  {Function} fn    Event handler
  @param  {String}   id    [Optional / Recommended] The id for the listener
  @param  {String}   scope [Optional / Recommended] The id of the object or element to be set as 'this'
  @param  {String}   st    [Optional] Application state, default is current
  @return {Mixed}          Primitive