How can I use express-validator for async validations?

How can I use express-validator for async validations?

You can use the check function from express-validator along with async functions to validate inputs. For example, you can create an async validation function that checks if a user exists in the database.

Can you show me 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 creating the user
});

This code 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. Just ensure to handle the results collectively in your route handler.