react 断网提示

react 断网提示，
断网，恢复网络时进行的操作

  // 断网提示
  useEffect(() => {
    
    
    let timer: NodeJS.Timer
    const online = () => {
    
    
      // 网络恢复
      timer && clearInterval(timer)
    }
    const offline = () => {
    
    
      timer && clearInterval(timer)
      timer = setInterval(() => {
    
    
        if (window.navigator.onLine === true) {
    
    
          message.success('网络恢复正常')
        } else {
    
    
          message.success('网络异常')
        }
      }, 3000)
    }

    window.addEventListener('online', online)
    window.addEventListener('offline', offline)

    return () => {
    
    
      timer && clearInterval(timer)
      window.removeEventListener('online', online)
      window.removeEventListener('offline', offline)
    }
  }, [])