Timespan.js

var Timespan = function(milliseconds) {
  this.milliseconds = milliseconds;
  this.seconds = this.milliseconds / 1000;
  this.minutes = this.seconds / 60;       
  this.hours = this.minutes / 60;
  this.days = this.hours / 24;
  this.weeks = this.days / 7;
  this.months = this.days / 30;
  this.years = this.months / 12;
  this.centuries = this.years / 100;
  this.millenia = this.years / 1000;
  
  return this;        
};

Timespan.zero_pad = function(value, length) {
  value = value.toString();
  
  while (value.length < length)
    value = '0' + value;
    
  return value;
};

Timespan.prototype.toString = function() {
  return Timespan.zero_pad(Math.floor(this.days), 2) + ':' 
       + Timespan.zero_pad(Math.floor(this.hours) % 24, 2) + ':' 
       + Timespan.zero_pad(Math.floor(this.minutes) % 60, 2) + ':' 
       + Timespan.zero_pad(Math.floor(this.seconds) % 60, 2) + '.' 
       + Timespan.zero_pad(Math.floor(this.milliseconds) % 1000, 3);
};