状态模式

允许一个对象在其内部状态改变时改变它的行为，对象看起来似乎修改了它的类。（开关灯）

状态模式的通用结构：

在一个Light的构造函数中，我们要创建每一个状态类的实例对象，Context将持有这些状态对象引用，以便把请求委托给状态对象。

//关灯
var OffLightState = function( light ){
    this.light = light; 
}

OffLightState.prototype.buttonWasPress = function(){
    console.log('弱光');
    this.light.setCurrState = ( this.light.weakLightState );
}
//弱光
var WeakLightState = function( light ){
    this.light = light; 
}

WeakLightState.prototype.buttonWasPress = function(){
    console.log('强光');
    this.light.setCurrState = ( this.light.StrongLightState );
}
var Light = function() {
    this.offLightState = new OffLightState( this );
    this.weakLightState = new WeakLightState( this );
    this.strongLightState = new StrongLightState( this );
    this.button = null;
};

Light.prototype.init = function(){
    var button = document.createElement('button'), self = this;
    this.button = document.body.appendChild( button );
    this.button.innerHTML = '开关';
    this.currState = this.offLightState;   //设置默认状态

    this.button.onclick = function(){
        self.currState.buttonWasPress();
    }
}

Light.prototype.setCurrState = function( newState ){
    this.currState = newState;
}

为避免一个对象遗漏方法的 技巧是：

var State = function(){};
State.prototype.buttonWasPressed = function(){
    throw new Error('父类的buttonWasPressed方法必须被重写');
}
var SupperStrongLightState = function( light ){
    this.light = light;
}

SupperStrongLightState.prototype = new State();

SupperStrongLightState.prototype.buttonWasPressed = function(){  //这里需要重写

}

JavaScript版本的状态机。

JS可以很方便的使用委托技术，并不需要事先让一个对象持有另一个对象。下面的状态机通过Function.prototype.call方法直接把请求委托给某在字面量对象来执行。

var Light = function() {
    this.currState = FSW.off;  //设置当前状态
    this.button = null;
};

Light.prototype.init = function(){
    var button = document.createElement('button'), self = this;
    this.button = document.body.appendChild( button );
    this.button.innerHTML = '已关灯';

    this.button.onclick = function(){
        self.currState.buttonWasPress.call( self );
    }
}
var FSW = {
    off:{
        buttonWasPress: function(){
            console.log('关灯');
            this.button.innerHTML = '下一次按我是开灯';
            FSW.currState = FSW.on;
        }
    },
    on:{
        buttonWasPress: function(){
            console.log('开灯');
            this.button.innerHTML = '下一次按我是关灯';
            FSW.currState = FSW.off;
        }
    }
}