Question

In a javascript code I develop, some function should be called every 1 second. But to be sure that this operation takes place every 1 second, the following code is utilized:

setInterval(doIt, 500);
function doIt() {
    var now = (new Date()).getTime();
    if(lastUpdate + 1000 >= now) {
       /// code...
       lastUpdate = now;
    }
}

As far as I know setInterval(doIt, 1000) doesn’t always mean that it’s called every one second.

Is the above solution is a valid one? If not, what do you recommend?

Answer 1

You could use setTimeout instead of setInterval, and make dynamic adjustments each time your function is called. The idea is to set the timeout for a number of milliseconds sufficient to carry you to the next second boundary.

function timeoutFunc() {
  // do interesting things
  var time = new Date().getTime();
  setTimeout(timeoutFunc, 1000 - time % 1000);
}

You’d start it off with:

setTimeout(timeoutFunc, 1000 - new Date().getTime() % 1000);

Synchronizing with the server seems like a bad idea, because you have no way of knowing whether the client clock is synchronized to anything (like the NTP server network). If it’s not, then you server synchronizations are going to make things look wrong at the client, because the client clock will always be what seems right.