JavaScript设计模式_13_状态模式

状态模式是一种根据事物内部状态的改变，从而改变事物行为的一种模式。

/**
 * pre:状态模式
 */
//---------- 示例1 ----------------
/**
 * 模拟电灯开关
 */
var Light = function() {
    this.state = "off";
    this.button = null;
};
Light.prototype.init = function() {
    var button = document.createElement("button");
    var _self = this;
    button.innerHTML = "开关";
    this.button = document.body.appendChild(button);
    this.button.onclick = function() {
        _self.buttonWasPressed();
    };
};
Light.prototype.buttonWasPressed = function() {
    var _self = this;
    var onEvent = function() {
        _self.state = "on";
        console.log("开灯");
    };
    var offEvent = function() {
        _self.state = "off";
        console.log("关灯");
    };
    var operations = {
        "off": onEvent,
        "on": offEvent
    }
    return operations[_self.state]();
};
var light = new Light();
light.init();
//----------- 示例2 --------
/**
 * [分析]：有另外一种电灯，按一次打开弱光，按两次打开强光，按三次关闭电灯。
 * 实现这一功能，我们需要对buttonWasPressed方法内部进行改造，增加另外一种状态事件。
 * 试想，如果在程序中，有N多种状态的切换，我们是不是要定义N多种状态，以及每种状态切换所发生的事件。
 * 若其中一个状态发生改变，还得去修改buttonWasPressed方法，使得复用性和可维护性大大降低。
 * 使用状态模式改写代码：
 */
var offLightState = function(light) {
    this.light = light;
};
offLightState.prototype.buttonWasPressed = function() {
    console.log("弱光");
    this.light.setCurrentState(this.light.weakLightState);
};
var weakLightState = function(light) {
    this.light = light;
};
weakLightState.prototype.buttonWasPressed = function() {
    console.log("强光");
    this.light.setCurrentState(this.light.strongLightState);
};
var strongLightState = function(light) {
    this.light = light;
};
strongLightState.prototype.buttonWasPressed = function() {
    console.log("超级强光");
    this.light.setCurrentState(this.light.superStrongLightState);
};
var superStrongLightState = function(light) {
    this.light = light;
};
superStrongLightState.prototype.buttonWasPressed = function() {
    console.log("关灯");
    this.light.setCurrentState(this.light.offLightState);
};
var Light = function() {
    this.offLightState = new offLightState(this);
    this.weakLightState = new weakLightState(this);
    this.strongLightState = new strongLightState(this);
    this.superStrongLightState = new superStrongLightState(this);
    this.currentState = null; // 当前状态
    this.button = null; // 开关
};
Light.prototype.setCurrentState = function(state) {
    this.currentState = state;
};
Light.prototype.init = function() {
    var _self = this;
    var button = document.createElement("button");
    button.innerHTML = "开关";
    this.button = document.body.appendChild(button);
    this.currentState = this.offLightState;
    this.button.onclick = function() {
        _self.currentState.buttonWasPressed();
    };
};
var light = new Light();
light.init();
//---------------- 示例3 ----------------
/**
 * 使用对象字面量重写
 */
var Light = function() {
    this.currentState = FSM.off;
    this.button = null;
};
var FSM = {
    "off": {
        buttonWasPressed: function() {
            console.log("弱光");
            this.currentState = FSM.weak;
        }
    },
    "weak": {
        buttonWasPressed: function() {
            console.log("强光");
            this.currentState = FSM.strong;
        }
    },
    "strong": {
        buttonWasPressed: function() {
            console.log("关灯");
            this.currentState = FSM.off;
        }
    }
};
Light.prototype.init = function() {
    var _self = this;
    var button = document.createElement("button");
    button.innerHTML = "开关";
    this.button = document.body.appendChild(button);
    this.button.onclick = function() {
        _self.currentState.buttonWasPressed.call(_self);
    };
};
var light = new Light();
light.init();
//------------- 示例4 --------------
/**
 * 使用委托进行重写
 */
var delegate = function(client, delegation) {
    return {
        "buttonWasPressed": function() {
            delegation.buttonWasPressed.apply(client, arguments);
        }
    };
};
var Light = function() {
    this.button = null;
    this.offLightState = delegate(this, FSM.off);
    this.weakLightState = delegate(this, FSM.weak);
    this.strongLightState = delegate(this, FSM.strong);
    this.currentState = this.offLightState;
};
var FSM = {
    "off": {
        "buttonWasPressed": function() {
            console.log("弱光");
            this.currentState = this.weakLightState;
        }
    },
    "weak": {
        "buttonWasPressed": function() {
            console.log("强光");
            this.currentState = this.strongLightState;
        }
    },
    "strong": {
        "buttonWasPressed": function() {
            console.log("关灯");
            this.currentState = this.offLightState;
        }
    }
};
Light.prototype.init = function() {
    var _self = this;
    var button = document.createElement("button");
    button.innerHTML = "开关";
    this.button = document.body.appendChild(button);
    this.button.onclick = function() {
        _self.currentState.buttonWasPressed.call(_self);
    };
}
var light = new Light();
light.init();
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原文地址：https://www.cnblogs.com/stinchan/p/7065432.html