How can I create custom validators in express-validator?

How can I create custom validators in express-validator?

You can create custom validators in express-validator by using the check function along with a custom validation function.

Can you show me an example of a custom validator?

Sure! Here's a simple example:

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

const customValidator = (value) => {
    if (!/^[a-zA-Z0-9]+$/.test(value)) {
        throw new Error('Only alphanumeric characters are allowed.');
    }
    return true;
};

app.post('/submit', [
    body('username').custom(customValidator)
], (req, res) => {
    // Handle request
});

What if I want to validate an array of values?

You can use the isArray method along with a custom validator for each item in the array. Here's an example:

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

app.post('/submit', [
    body('tags').isArray().custom((tags) => {
        tags.forEach(tag => {
            if (!/^[a-zA-Z]+$/.test(tag)) {
                throw new Error('Tags must be alphabetic.');
            }
        });
        return true;
    })
], (req, res) => {
    // Handle request
});