实现简单请求与预检请求与携带cookie

express的代码

const express = require('express');
const app = express();     
// 跨域 CORS
app.use(require('./corsMiddleware'));
app.use('/api/student', require('./api/student'));
// 处理错误的中间件函数
app.use(require('./errorMiddleware'));
app.listen(5000, () => {
  console.log('监听端口');
});

判断请求

const allowOrigin = ['null', 'http://127.0.0.1:5500'];
module.exports = (req, res, next) => {
  //判断预检请求
  if(req.method === 'OPTIONS') {
    res.header(
      'Access-Control-Allow-Methods',
      req.headers['access-control-request-method']
    );
    res.header(
      'Access-Control-Allow-Headers',
      req.headers['access-control-request-headers']
    );
  }
  // 当携带cookie
  res.header('Access-Control-Allow-Credentials', true);
  // 判断简单请
  if ('origin' in req.headers && allowOrigin.includes(req.headers['origin'])) {
    res.header('Access-Control-Allow-Origin', req.headers['origin']);
  }
  next()
}