Detecting changes to system time in JavaScript

Question

How can I write a script to detect when a user changes their system time in JS?

Answer 1

Check in an interval function that the time has not changed too much:

function getTime()  {
  var d = new Date();
  return d.getTime();
}

function checkTime()  {
  if (Math.abs(getTime() - oldtime) > 2000)  {  // Changed by more than 2 seconds?
    alert("You changed the time!");
  }
  oldtime = getTime();
}

var oldtime = getTime();
setInterval(checkTime, 1000);  // Check every second that the time is not off

Tested on Windows with Opera & FF and works flawlessly.