var Memento = function(state){
  var _state = state;
  this.getState = function(){
    return _state;
  }
}
 
var Originator = function(){
  var _state;
  this.setState = function(state){
    _state = state;
  }
  this.getState = function(){
    return _state;
  }
  this.saveStateToMemento = function(){
    return new Memento(_state)
  }
  this.getStateFromMemento = function(memento){
    _state = memento.getState();
  }
}
 
var CareTaker = function(){
  var _mementoList = [];
  this.add = function(memento){
    _mementoList.push(memento);
  }
  this.get = function(index){
    return _mementoList[index];
  }
}
 
var originator = new Originator();
var careTaker = new CareTaker();
originator.setState("State 1");
originator.setState("State 2");
careTaker.add(originator.saveStateToMemento());
originator.setState("State 3");
careTaker.add(originator.saveStateToMemento());
originator.setState("State 4");
 
console.log("当前状态: " + originator.getState());
// 当前状态: State 4
originator.getStateFromMemento(careTaker.get(0));
console.log("恢复第一次保存状态: " + originator.getState());
// 恢复第一次保存状态: State 2
originator.getStateFromMemento(careTaker.get(1));
console.log("恢复第二次保存: " + originator.getState());
// 恢复第二次保存: State 3