How to execute a function only if that function isn't already running?

[londres9b]

I have a function that runs every time the user changes something. But sometimes the user will have to change multiple things and I don't want to call the function 2 or more times..
How can I make it execute only if it isn't already running?

[Dormilich]

how did you define the onchange event?

[londres9b]

It's a checkbox and whenever it's changed the function executes.

onchange="result()"

[Dormilich]

that actually fires? well, you can’t avoid that each checkbox fires when it is clicked. the only way out would be a final "calculate result now" button. (between (un)checking two checkboxes is too much time for the first event to know that there will be another event soon)

you could try to define a blur event on the form, but that is not reliable, esp. if you don’t use a mouse (e.g. when tabbing through the options)

[londres9b]

So there isn't any way to check if a function is running?

[Dormilich]

how long does your function run?

regular functions run between 0 and 5 ms.

[londres9b]

The function checks which checkboxes are checked and makes an ajax request to update a table.

So you can see why I wanted to do this, I would wait for a second or two and then check which checkboxes are checked.

[Dormilich]

you can’t test whether a regular function currently runs (JavaScript would have to be multi-threaded to do that, which is just not the way it is programmed).

in case of AJAX I see only the option to abort the first request, but unless you have a very slow internet connection or a massively complex server script behind, this will be finished before the second event occurs.

maybe I could imagine some kind of request stacking with timeouts, though that sounds rather complicated.

[londres9b]

Maybe if I set the result() function to execute automatically every 3 seconds, instead of the onchange trigger..

Okey, thanks for your help.

[Dormilich]

but then you would make an AJAX request every 3 seconds (constantly adding up to your transfer volume and server load), no matter whether there was a checkbox changed or not.

[londres9b]

yes, I know, I'll leave at is was and include something to prevent the user from clicking the checkboxes while the function is running.

[Dormilich]

that would be mean towards the user. your function probably runs faster than the user clicks another option.

[londres9b]

Then I guess I'll go back to how it was

[rnd me]

sometimes the user will have to change multiple things and I don't want to call the function 2 or more times..
How can I make it execute only if it isn't already running?

your function needs a few lines at the top and bottom:

function myChanger(){
 if(arguments.callee.busy){return;}
 arguments.callee.busy=true;
 
 //... now do the slow stuff like normal

 arguments.callee.busy = false;
}//end myChanger()

now, if it fires again while the middle is already running, it returns without proceeding further.