Javascript Date serialize()

Date.get = function( str ){
 var arr = str.split("-"),
  d = new Date();//from   w  ww .j  a  v  a 2 s .  co m
 
 d.setFullYear( arr[0], arr[1] - 1, arr[2] );
 d.setHours(0,0,0,0);
 return d;
};
Date.prototype.serialize = function(){
 var m = this.getMonth() + 1;
 return this.getFullYear() + "-" + (m > 9 ? m : "0"+m ) + "-" + this.getDate();
};
Date.diff = function( date1, date2  ){

 return Math.floor( (date1.getTime() - date2.getTime()) / (1000 * 3600 * 24) );

 var year=date1.getFullYear() - date2.getFullYear();
 var month=date1.getMonth() - date2.getMonth();
 var day=date1.getDate() - date2.getDate();    
 return year*12*30+month*30+day;
};