Playing around with more accurate JS timeouts for long durations with system time as reference

accurate.js

/**
 * Long timeouts that remain accuracy.
 */

// When the final system adjusted timer kicks in
var FINAL_COUNTDOWN = 2000;

var accurate = {};

accurate.setTimeout = function(fn, t) {
  var begin = new Date().getTime();
  var end = begin + t;
  setTimeout(function() {
    // Measure again properly
    var now = new Date().getTime();
    setTimeout(fn, end - now);
  }, t - FINAL_COUNTDOWN);
}


accurate.testTimeout = function(t) {
  var d = new Date();
  console.log('Beginning timeout test at '+ d);
  var begin = d.getTime();
  var end = begin + t;
  setTimeout(function() {
    var now = new Date().getTime();
    console.log('setTimeout error: '+ (now - end));
  }, t);
  accurate.setTimeout(function() {
    var now = new Date().getTime();
    console.log('accurate.setTimeout error: '+ (now - end));
  }, t);
}