Trip

gistfile1.txt

function trip (s) {
  if ('tripIntervalId' in window) {
    clearInterval(window.tripIntervalId);
  }
  
  var filters = ['invert(100%)', 'none']
  
  var counter = 0;

  function swap() {
    var i = counter % 2;
    counter++;
    document.body.style.webkitFilter = filters[i];
  }
  
  window.tripIntervalId = setInterval(swap, s || 60);
}