settimeout.js

// if we have
function do() {
  // thing that takes 100ms - 2s depending on browser
}

// Instead of:
setInterval(do, 500) // pray it doesn't lock the browser


// Do this:
function doAndTick() {
  do();
  setTimeout(doAndTick, 100);
}
doAndTick();

// It will not run exactly every 500, but it guarantees 100ms of downtime for the browser