APP推送平台限时秒杀

import React, { useState, useEffect } from 'react';

function Countdown({ endTime }) {
  const [timeLeft, setTimeLeft] = useState(calculateTimeLeft(endTime));

  useEffect(() => {
    const timer = setTimeout(() => {
      setTimeLeft(calculateTimeLeft(endTime));
    }, 1000);

    return () => clearTimeout(timer);
  }, [endTime]);

  function calculateTimeLeft(endTime) {
    const difference = new Date(endTime).getTime() - new Date().getTime();
    if (difference <= 0) return { days: 0, hours: 0, minutes: 0, seconds: 0 };
    const days = Math.floor(difference / (1000 * 60 * 60 * 24));
    const hours = Math.floor((difference % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60));
    const minutes = Math.floor((difference % (1000 * 60 * 60)) / (1000 * 60));
    const seconds = Math.floor((difference % (1000 * 60)) / 1000);
    return { days, hours, minutes, seconds };
  }

  return (
    <div>
      <span>{timeLeft.days}天</span>
      <span>{timeLeft.hours}小时</span>
      <span>{timeLeft.minutes}分钟</span>
      <span>{timeLeft.seconds}秒</span>
    </div>
  );
}

export default Countdown;

const express = require('express');
const app = express();
const bodyParser = require('body-parser');
const { Pool } = require('pg');

const pool = new Pool({
  user: 'your_db_user',
  host: 'your_db_host',
  database: 'your_db_name',
  password: 'your_db_password',
  port: 5432,
});

app.use(bodyParser.json());

app.post('/seckill', async (req, res) => {
  const { productId, userId } = req.body;
  const client = await pool.connect();
  try {
    await client.query('BEGIN');
    const { rows } = await client.query('SELECT stock FROM products WHERE id = $1 FOR UPDATE', [productId]);
    if (rows[0].stock <= 0) {
      return res.status(400).send('Out of stock');
    }
    await client.query('UPDATE products SET stock = stock - 1 WHERE id = $1', [productId]);
    await client.query('INSERT INTO orders (product_id, user_id) VALUES ($1, $2)', [productId, userId]);
    await client.query('COMMIT');
    res.send('Success');
  } catch (e) {
    await client.query('ROLLBACK');
    res.status(500).send(e.message);
  } finally {
    client.release();
  }
});

app.listen(3000, () => console.log('Server running on port 3000'));