13、状态模式

1、特点

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。

2、demo

电灯的开、亮度、关

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

OffLightState.prototype.buttonWasPressed = function() {
    console.log('弱光'); // offLightState 对应的行为
    this.light.setState(this.light.weakLightState); // 切换状态到weakLightState
};
// WeakLightState：
var WeakLightState = function(light) {
    this.light = light;
};

WeakLightState.prototype.buttonWasPressed = function() {
    console.log('强光'); // weakLightState 对应的行为
    this.light.setState(this.light.strongLightState); // 切换状态到strongLightState
};
// StrongLightState：
var StrongLightState = function(light) {
    this.light = light;
};

StrongLightState.prototype.buttonWasPressed = function() {
    console.log('关灯'); // strongLightState 对应的行为
    this.light.setState(this.light.offLightState); // 切换状态到offLightState
};

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; // 设置当前状态
    this.button.onclick = function() {
        self.currState.buttonWasPressed();
    }
};

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

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

参考文献：《JavaScript设计模式与开发实践》