Question

My ASP.NET MVC page uses JavaScript/jQuery to poll my database every second.

This is working but I want to make sure that, if there is a delay, my timer handler won’t get called again before it has returned.

In there any trick to this other than storing the timer ID in a global variable, clearing the timer in my handler, and restarting it when my handler is done.

NOTE: I realize every second seems frequent but this code is polling my server after submitting a credit card payment. Normally, it will only run for a second or so, and I don’t want the user to wait any longer than necessary.

Answer 1

Polling every second? That’s quite heavy!

That aside, you won’t have this issue when setTimeout is used instead of setInterval. The latter ensures that a piece of code is run x times given a interval, while the former ensures that there’s a delay of at least x milliseconds.

function some_poller() {
    $.ajax({
       url: '/some_page',
       success: function() {
           setTimeout(some_poller, 1000);
       },
       error: function() { // Also retry when the request fails
           setTimeout(some_poller, 1000);
       }
    });
}

// Init somewhere
some_poller();