gistfile1.js

Object.extend(Date.prototype, {
  strftime: function(format) {
    var day = this.getDay(), month = this.getMonth();
    var hours = this.getHours(), minutes = this.getMinutes();

    return format.gsub(/\%([aAbBcdDHiImMpSwyY])/, function(part) {
      switch(part[1]) {
        case 'a': return $w("Sun Mon Tue Wed Thu Fri Sat")[day]; break;
        case 'A': return $w("Sunday Monday Tuesday Wednesday Thursday Friday Saturday")[day]; break;
        case 'b': return $w("Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec")[month]; break;
        case 'B': return $w("January February March April May June July August September October November December")[month]; break;
        case 'c': return this.toString(); break;
        case 'd': return this.getDate(); break;
        case 'D': return this.getDate().pad(2); break;
        case 'H': return hours.pad(2); break;
        case 'i': return (hours === 12 || hours === 0) ? 12 : (hours + 12) % 12; break;
        case 'I': return ((hours === 12 || hours === 0) ? 12 : (hours + 12) % 12).pad(2); break;
        case 'm': return (month + 1).pad(2); break;
        case 'M': return minutes.pad(2); break;
        case 'p': return hours > 11 ? 'PM' : 'AM'; break;
        case 'S': return this.getSeconds().pad(2); break;
        case 'w': return this.getWeek(); break;
        case 'y': return (this.getFullYear() % 100).pad(2); break;
        case 'Y': return this.getFullYear().toString(); break;
      }
    }.bind(this));
  },
  
  toShort: function() {
    return this.strftime('%Y-%m-%D');
  },
  
  human: function() {
    var today = Date._today || (Date._today = Date.today().beginningOfDay()),
      day = this.beginningOfDay(), dayAsTime = day.getTime(), todayAsTime = today.getTime();
    if(todayAsTime == dayAsTime){
      return "today";
    } else if(today.yesterday().getTime() == dayAsTime) {
      return "yesterday"
    } else if(dayAsTime > todayAsTime - (180*(24*60*60*1000))) { // half a year ago
      return day.strftime('%b %d');
    } else {
      return day.strftime('%b %d, %Y');
    }
  },

  beginningOfDay: function() {
    return new Date(this.getFullYear(), this.getMonth(), this.getDate());
  },
  
  addDays: function(days){
    return new Date(this.getTime() + (days*1000*60*60*24));
  },
  
  tomorrow: function(){
    return this.addDays(1);
  },
  
  yesterday: function(){
    return this.addDays(-1);
  },
  
  beginningOfMonth: function(){
    return new Date(this.getFullYear(), this.getMonth(), 1);
  },
  
  endOfMonth: function(){
    return new Date(this.getFullYear(), this.getMonth()+1, 0);
  },
  
  previousMonth: function(){
    return new Date(this.getFullYear(), this.getMonth()-1, 1);
  },
  
  nextMonth: function(){
    return new Date(this.getFullYear(), this.getMonth()+1, 1);
  },
  
  getWeek: function() {
    var ref = new Date(this.getFullYear(), 0, 1);
    return Math.ceil((((this - ref) / 86400000) + ref.getDay()) / 7);
  },
  
  sundayOfWeek: function(){
    return this.addDays(-this.getDay()).beginningOfDay();
  },
  
  mondayOfWeek: function(){
    return this.addDays(-this.getDay()+1).beginningOfDay();
  },
  
  previousWeekSunday: function(){
    return this.addDays(-(this.getDay()+7)).beginningOfDay();
  },
  
  previousWeekMonday: function(){
    return this.addDays(-(this.getDay()+6)).beginningOfDay();
  },
  
  nextWeekSunday: function(){
    return this.addDays(7-this.getDay()).beginningOfDay();
  },
  
  nextWeekMonday: function(){
    return this.addDays(7-this.getDay()+1).beginningOfDay();
  },
  
  isToday: function() {
    return this.isDate(new Date());
  },
  
  isDate: function(date) {
    return (
      this.getFullYear() == date.getFullYear() && 
      this.getMonth() == date.getMonth() && 
      this.getDate() == date.getDate()
    );
  }
});

Date.today = function(){
  return new Date();
}

My fav quote of all time for when you guys bellow "Premature optimization":

It's unacceptable to use the aforementioned "don't optimize prematurely" mantra as an excuse to write bad code, which brings me to this point. While your code should be as readable as possible, it shouldn't be blatantly un-optimized.