如何在express-validator中创建自定义异步验证器？

npm install express-validator

const { body, validationResult } = require('express-validator');

const customAsyncValidator = (value) => {
  return new Promise((resolve, reject) => {
    // 异步操作，例如数据库查询
    // 如果验证成功，调用resolve()
    // 如果验证失败，调用reject()，并传递一个错误消息
  });
};

app.post('/example', [
  body('field').custom(customAsyncValidator)
], (req, res) => {
  // 处理请求
});

app.post('/example', [
  body('field').custom(customAsyncValidator)
], (req, res) => {
  const errors = validationResult(req);
  if (!errors.isEmpty()) {
    // 处理验证错误
  } else {
    // 验证通过，继续处理请求
  }
});