实现一个带有 once 的 pubsub 类.使用 JavaScript 实现

以下是 JavaScript 代码实现一个带有 "once" 功能的 pubsub 类：

class Pubsub {
  constructor() {
    this.subscribers = {}
  }

  subscribe(event, callback) {
    if (!this.subscribers[event]) {
      this.subscribers[event] = []
    }
    this.subscribers[event].push(callback)
  }

  once(event, callback) {
    const wrapper = (...args) => {
      callback(...args)
      this.off(event, wrapper)
    }
    this.subscribe(event, wrapper)
  }

  off(event, callback) {
    if (!this.subscribers[event]) {
      return
    }
    this.subscribers[event] = this.subscribers[event].filter(
      item => item !== callback
    )
  }

  publish(event, ...args) {
    if (!this.subscribers[event]) {
      return
    }
    this.subscribers[event].forEach(callback => callback(...args))
  }
}

使用方法：

const pubsub = new Pubsub()

const callback = (data) => {
  console.log(`Received data: ${data}`)
}

pubsub.subscribe('event', callback)
pubsub.publish('event', 'Hello World!')

// Output: Received data: Hello World!

pubsub.once('event', (data) => {
  console.log(`Received data once: ${data}`)
})
pubsub.publish('event', 'Hello World!')

// Output:
// Received data: Hello World!
// Received data once: Hello World!

pubsub.publish('event', 'Hello World!')

// Output:
// Received data: Hello World!

这个 pubsub 类提供了 "subscribe"、"once"、"off" 和 "publish" 四个方法，它们分别用于订阅、只订阅一次、取消订阅和发布事件。