在JS中的设计模式的单例模式、策略模式、代理模式、原型模式浅讲

1. 单例模式（Singleton Pattern）

确保一个类只有一个实例，并提供一个全局访问点。

示例代码：

class Singleton {constructor() {if (Singleton.instance) {return Singleton.instance;}Singleton.instance = this;this.data = [];}addData(value) {this.data.push(value);}getData() {return this.data;}
}const singleton1 = new Singleton();
const singleton2 = new Singleton();singleton1.addData('value1');console.log(singleton1.getData()); // ['value1']
console.log(singleton2.getData()); // ['value1'] - Both are the same instance

2. 策略模式（Strategy Pattern）

定义一系列算法，把它们一个个封装起来，并且使它们可以互换。

示例代码：

class Context {constructor(strategy) {this.strategy = strategy;}executeStrategy(a, b) {return this.strategy.execute(a, b);}
}class AdditionStrategy {execute(a, b) {return a + b;}
}class SubtractionStrategy {execute(a, b) {return a - b;}
}const context = new Context(new AdditionStrategy());
console.log(context.executeStrategy(5, 3)); // 8context.strategy = new SubtractionStrategy();
console.log(context.executeStrategy(5, 3)); // 2

3. 代理模式（Proxy Pattern）

为其他对象提供一种代理以控制对这个对象的访问。

示例代码：

class RealObject {request() {console.log('Request made to RealObject');}
}class Proxy {constructor(realObject) {this.realObject = realObject;}request() {console.log('Request intercepted by Proxy');this.realObject.request();}
}const realObject = new RealObject();
const proxy = new Proxy(realObject);proxy.request(); // Request intercepted by Proxy// Request made to RealObject

4. 原型模式（Prototype Pattern）

通过复制现有的实例来创建新对象，而不是通过实例化新对象。

示例代码：

class Prototype {constructor() {this.primitive = 0;this.object = { a: 1 };}clone() {const clone = Object.create(this);clone.object = Object.assign({}, this.object);return clone;}
}const original = new Prototype();
original.primitive = 1;
original.object.a = 2;const copy = original.clone();
console.log(copy.primitive); // 1
console.log(copy.object.a);  // 2