timespan in js

gistfile1.js

function timespan(start, end) {
  if (typeof end === "undefined") {
    end = start;
    start = Date.now();
  }

  if (start !== null && typeof start === "object" && start.getTime) {
    start = start.getTime();
  } 

  if (end !== null && typeof end === "object" && end.getTime) {
    end = end.getTime();
  } 

  start = +start;
  end = +end;

  if (isNaN(start) || isNaN(end))
    throw new Error("Cannot convert arguments into numbers");

  var t = Math.abs(end - start);

  return {
    milliseconds: ((t % 1000) / 100) |0,
    seconds: ((t / 1000) % 60) |0,
    minutes: ((t / 60000) % 60) |0,
    hours: ((t / 360000) % 24) |0,
    toString: function() {
      var h = "0" + this.hours, m = "0" + this.minutes, s = "0" + this.seconds;
      var ms = "00" + this.milliseconds;
      return h.substr(-2) + ":" + m.substr(-2) + ":" + s.substr(-2) + "." + ms.substr(-3);
    }
  }
}