(3).day.ago

time.js

function definePropertiesOfObjects(objects, values){
  for (var i = 0; i < objects.length; i++) {
    Object.defineProperties(objects[i], values);
  }
}

function defineProperty(){
  Object.defineProperty.apply(null, arguements);
}

definePropertiesOfObjects([Number.prototype], {
  week: {
    get: function(){
      this.__milliseconds = this * 1000 * 3600 * 24 * 7;
      return this;
    }
  },
  day: {
    get: function(){
      this.__milliseconds = this * 1000 * 3600 * 24;
      return this;
    }
  },
  ago: {
    get: function(){
      return new Date(Date.now() - this.__milliseconds);
    }
  },
  next: {
    get: function(){
      return new Date(Date.now() + this.__milliseconds);
    }
  }
});

console.log((3).week.ago);
console.log((3).day.next);