SOURCE

var delegate = function(client,delegation){
    return {
        buttonWasPressed:function(){
            return delegation.buttonWasPressed.apply(client,arguments)
        }
    }
}

var FSM = {
    off:{
        buttonWasPressed:function(){
            console.log("关灯")
            this.button.innerHTML="下一次按我是开灯";
            this.currState = this.onState;
        }
    },
    on:{
        buttonWasPressed:function(){
            console.log("开灯")
            this.button.innerHTML="下一次按我是关灯";
            this.currState = this.offState;
        }
    }
}

var Light = function(){
    this.offState = delegate(this,FSM.off)
    this.onState = delegate(this,FSM.on)
    this.currState = this.offState
    this.button = null;
}
Light.prototype.init = function(){
    var button = document.createElement('button'),
    self = this;
    button.innerHTML = "已关灯"
    this.button = document.appendChild(button)
    this.button.onclick = function(){
        self.currState.buttonWasPressed()
    }
}

var light = new Light()
light.init()