let myVariable = 10;

const obj = {
  get value() {
    return myVariable;
  },
  set value(newValue) {
    myVariable = newValue;
    console.log('Variable value changed:', newValue);
  }
};

console.log(obj.value); // 输出：10
obj.value = 20; // 输出：Variable value changed: 20
console.log(obj.value); // 输出：20

let myVariable = 10;

const handler = {
  get(target, property) {
    return target[property];
  },
  set(target, property, value) {
    target[property] = value;
    console.log('Variable value changed:', value);
    return true;
  }
};

const proxy = new Proxy({}, handler);
proxy.value = myVariable;

console.log(proxy.value); // 输出：10
proxy.value = 20; // 输出：Variable value changed: 20
console.log(proxy.value); // 输出：20

class Observable {
  constructor() {
    this.observers = [];
  }

  addObserver(observer) {
    this.observers.push(observer);
  }

  removeObserver(observer) {
    const index = this.observers.indexOf(observer);
    if (index !== -1) {
      this.observers.splice(index, 1);
    }
  }

  notifyObservers(value) {
    this.observers.forEach(observer => observer.update(value));
  }
}

class Variable extends Observable {
  constructor(value) {
    super();
    this.value = value;
  }

  setValue(newValue) {
    this.value = newValue;
    this.notifyObservers(newValue);
  }
}

class Observer {
  update(value) {
    console.log('Variable value changed:', value);
  }
}

const myVariable = new Variable(10);
const observer = new Observer();
myVariable.addObserver(observer);

console.log(myVariable.value); // 输出：10
myVariable.setValue(20); // 输出：Variable value changed: 20
console.log(myVariable.value); // 输出：20