错误隔离

// ❌ 没有超时，可能永远等待
async function callPaymentService() {
  return await paymentAPI.charge()
}

// ✅ 2秒超时，快速失败
async function callPaymentService() {
  return await Promise.race([
    paymentAPI.charge(),
    timeout(2000)
  ])
}

class CircuitBreaker {
  constructor(threshold = 5) {
    this.failureCount = 0
    this.threshold = threshold
    this.state = 'CLOSED' // CLOSED, OPEN, HALF_OPEN
  }

  async call(fn) {
    if (this.state === 'OPEN') {
      throw new Error('Circuit breaker is OPEN')
    }

    try {
      const result = await fn()
      this.onSuccess()
      return result
    } catch (error) {
      this.onFailure()
      throw error
    }
  }

  onSuccess() {
    this.failureCount = 0
    this.state = 'CLOSED'
  }

  onFailure() {
    this.failureCount++
    if (this.failureCount >= this.threshold) {
      this.state = 'OPEN'
      setTimeout(() => this.state = 'HALF_OPEN', 60000)
    }
  }
}

async function renderPage() {
  // 核心内容：必须成功
  const article = await getArticle()

  // 次要功能：失败后降级
  let recommendations = []
  try {
    recommendations = await getRecommendations()
  } catch (error) {
    // 降级：使用默认推荐
    recommendations = getDefaultRecommendations()
  }

  // 可选功能：失败后隐藏
  let comments = null
  try {
    comments = await getComments()
  } catch (error) {
    // 降级：不显示评论区
    comments = null
  }

  return render({ article, recommendations, comments })
}