node.js: setInterval() skipping calls

SetInterval functions in javascript are not accurate. You should try to use a high resolution timer.Building accurate Timers in javascript

Look at this doc: http://nodejs.org/api/timers.html#timers_settimeout_callback_delay_arg

It is important to note that your callback will probably not be called in exactly delay milliseconds - Node.js makes no guarantees about the exact timing of when the callback will fire, nor of the ordering things will fire in. The callback will be called as close as possible to the time specified.

This happens because application code blocks the event loop. All timers and I/O events can be handled only on the nextTick.

You can see this behaviour with this code:

setInterval(function() {
    console.log(Date.now());
    for (var i = 0; i < 100000000; i++) {
    }
}, 1);

Try to change iterations count and see results.

Ideally, the timer will be triggered exactly if the applications tick will last less than one ms. But this is not practicable in a real application.