Rails spinoffs - Dec 2005 - PeriodicalExecuter passing variables to the callback function

I trying to pass a variable to the call back function of when utilizing 
the PeriodicalExecuter function

ex.

new PeriodicalExecuter(refresh, 10);
works

but
new PeriodicalExecuter(refresh(id), 10);
works once then errors after the 10 seconds, I get "this.callback is 
not a function"

I trying to pass a variable to the call back function of when utilizing 
the PeriodicalExecuter function

ex.

new PeriodicalExecuter(refresh, 10);
works

but
new PeriodicalExecuter(refresh(id), 10);
works once then errors after the 10 seconds, I get "this.callback is 
not a function"

The difference is that in the first example you are passing a  
reference to the function "variable". In the second example you are  
actually executing the function ( which is why it works once ) and  
the returned result of the "refresh()" function is then passed to  
PeriodicalExecuter. ( which is probably null, which is why it  
fails ). So the order of operations for your second example is:

1) Execute refresh function and pass it the current value of id. Get  
the returned result
2) Pass the returned result as the first argument of new  
PeriodicalExecuter
3) PeriodicalExecuter tries to execute the returned result from the  
refresh function (which is not a function object, so it complains ).

To get around this you can create a new lambda function and pass that  
to PeriodicalExecuter. There are two ways to do this:

1) new PeriodicalExecuter( function(){refresh(id)}, 10 );

2) new PeriodicalExecuter( new
Function("refresh(''"+id+"'')"), 10 );

The "problem" with the first one is that when the PeriodicalExecuter  
gets called it will be called with whatever the CURRENT value of id  
is ( not the value of id at the time you created the  
PeriodicalExecuter ). This is probably not what you want. Which is  
you why you should use the second option which creates a new function  
dynamically ( basically it evals the string you pass into it ). So in  
the second example, if the current value of id was "elem1" it would  
create a function like:

	function()
	{
		refresh(''elem1'');
	}

which should work for you. They are called lambda function because  
they don''t have any names.

P.S. Here is a good reference on javascript functions in general:
	http://www.permadi.com/tutorial/jsFunc/

-John


On Dec 12, 2005, at 9:09 AM, Steven Albarracin wrote:
> I trying to pass a variable to the call back function of when  
> utilizing the PeriodicalExecuter function
>
> ex.
>
> new PeriodicalExecuter(refresh, 10);
> works
>
> but
> new PeriodicalExecuter(refresh(id), 10);
> works once then errors after the 10 seconds, I get "this.callback  
> is not a function"
>
> _______________________________________________
> Rails-spinoffs mailing list
> Rails-spinoffs-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails-spinoffs