js 实现 eventbus

实现 EventBus 的基本结构

EventBus 是一种发布/订阅模式，用于组件或模块间的通信。以下是一个简单的 EventBus 实现：

class EventBus {
  constructor() {
    this.events = {};
  }

  on(eventName, callback) {
    if (!this.events[eventName]) {
      this.events[eventName] = [];
    }
    this.events[eventName].push(callback);
  }

  emit(eventName, ...args) {
    if (this.events[eventName]) {
      this.events[eventName].forEach(callback => {
        callback(...args);
      });
    }
  }

  off(eventName, callback) {
    if (this.events[eventName]) {
      if (callback) {
        this.events[eventName] = this.events[eventName].filter(cb => cb !== callback);
      } else {
        delete this.events[eventName];
      }
    }
  }
}

使用示例

const eventBus = new EventBus();

// 订阅事件
eventBus.on('message', (text) => {
  console.log('Received:', text);
});

// 发布事件
eventBus.emit('message', 'Hello EventBus!');

// 取消订阅
const handler = (text) => console.log('Handler:', text);
eventBus.on('message', handler);
eventBus.off('message', handler);

支持一次性事件监听

可以通过扩展 on 方法或添加 once 方法实现一次性事件监听：

class EventBus {
  constructor() {
    this.events = {};
  }

  once(eventName, callback) {
    const onceWrapper = (...args) => {
      callback(...args);
      this.off(eventName, onceWrapper);
    };
    this.on(eventName, onceWrapper);
  }
}

// 使用示例
eventBus.once('greet', (name) => {
  console.log(`Hello ${name}, this will only run once!`);
});

eventBus.emit('greet', 'Alice'); // 触发
eventBus.emit('greet', 'Bob');   // 不触发

支持异步事件处理

可以通过 Promise 或 async/await 支持异步事件处理：

class AsyncEventBus extends EventBus {
  async emitAsync(eventName, ...args) {
    if (this.events[eventName]) {
      for (const callback of this.events[eventName]) {
        await callback(...args);
      }
    }
  }
}

// 使用示例
const asyncBus = new AsyncEventBus();
asyncBus.on('asyncEvent', async (data) => {
  await new Promise(resolve => setTimeout(resolve, 1000));
  console.log('Async processed:', data);
});

asyncBus.emitAsync('asyncEvent', 'Test Data');

支持事件优先级

可以通过扩展数据结构支持事件优先级：

class PriorityEventBus extends EventBus {
  on(eventName, callback, priority = 0) {
    if (!this.events[eventName]) {
      this.events[eventName] = [];
    }
    this.events[eventName].push({ callback, priority });
    this.events[eventName].sort((a, b) => b.priority - a.priority);
  }

  emit(eventName, ...args) {
    if (this.events[eventName]) {
      this.events[eventName].forEach(({ callback }) => {
        callback(...args);
      });
    }
  }
}

// 使用示例
const priorityBus = new PriorityEventBus();
priorityBus.on('priorityEvent', () => console.log('Default Priority'), 0);
priorityBus.on('priorityEvent', () => console.log('High Priority'), 10);
priorityBus.emit('priorityEvent');