How can I implement async validation with express-validator?

How can I implement async validation with express-validator?

You can use the check function along with a custom async validator. Would you like a code example?

Yes, please provide a code example.

Sure! Here's a simple example:

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

app.post('/user', [
  check('email').isEmail().withMessage('Must be a valid email'),
  check('username').custom(async (value) => {
    const user = await User.findOne({ username: value });
    if (user) {
      throw new Error('Username already in use');
    }
  })
], async (req, res) => {
  const errors = validationResult(req);
  if (!errors.isEmpty()) {
    return res.status(400).json({ errors: errors.array() });
  }
  // Proceed with user creation
});

This checks if the email is valid and if the username is already taken.

What if I want to validate multiple fields asynchronously?

You can chain multiple check functions for different fields. Each can have its own async validation logic.