function getDayOfWeek(){
var dayOfWeek = new Array("日","月","火","水","木","金","土");
return dayOfWeek[this.getDay()];
}
Date.prototype.getDayOfWeek = getDayOfWeek;

var today = new Date();
  with(document){
  write(today.getFullYear(),"年");
  write(today.getMonth() + 1,"月");
  write(today.getDate(),"日");
  write(" ",today.getDayOfWeek(),"曜日");
  }