setAccurateInterval

// Written by Robert 'rynti' Böhm, free to use by anyone

// Repeats a given function in a given interval.
// The difference between setAccurateInterval and setInterval is that this version
// preserves the original interval, as for example if your start a function on
// millisecond 0 with an interval of 1000, it will always try to execute the function
// on millisecond 1000, then 2000, then 3000, etc.
// The standard setInterval function however will always execute the given function,
// then wait 1000 milliseconds until it executes the function again. If the function
// always takes 20 milliseconds to process for instance, it will execute the given
// function on millisecond 1000, then 2020, then 3040, then 4060, etc.

// The parameter allowChoking can be used to avoid the (by default enabled) choke-
// prevention. This means that for example if you use an interval of 1 second, and
// the function takes 1.5 seconds to process, with choke prevention the interval
// will try to preserve the original interval, only executing the function on
// second 1, then second 3, then second 5, etc.

// If you don't want to use the default setTimeout function for waiting, you can pass
// your custom setTimeout function as a fourth parameter. The function parameters
// should match with the ones of the original setTimeout one.
function setAccurateInterval(callback, interval, allowChoking, timeoutFunction) {
  if (!timeoutFunction) timeoutFunction = setTimeout;
  var start = Date.now();
  var tick = function () {
    callback();
    start += interval;
    var target = start + interval;
    var diff = target - Date.now();
    if (!allowChoking) {
      while (diff < 0) {
        diff += interval;
        start += interval;
      }
    }
    timeoutFunction(tick, diff);
  };
  timeoutFunction(tick, interval);
}

// Example usage of setAccurateInterval
setAccurateInterval(function () {
  // Print the current timestamp:
  var start = Date.now();
  console.log('Processing started at ' + start);

  // Do something time-intensive:
  var s = "";
  for (var i = 0; i < 10000000; i++) { s += "a"; }

  // Print how long the function took to process:
  var end = Date.now();
  console.log('Processing took ' + (end - start) + 'ms');
}, 1000);