How can I implement custom validation in Formik?

How can I implement custom validation in Formik?

You can implement custom validation in Formik by using the validate prop or by creating a validation schema with Yup.

Can you show me an example of using Yup for validation?

Sure! Here's a simple example:

import * as Yup from 'yup';

const validationSchema = Yup.object().shape({
  email: Yup.string().email('Invalid email').required('Required'),
  password: Yup.string().min(6, 'Too Short!').required('Required'),
});

Then, pass this schema to the validationSchema prop in your Formik component.

What if I want to validate based on another field's value?

You can use the when method in Yup to create conditional validations. For example:

passwordConfirmation: Yup.string()
  .oneOf([Yup.ref('password'), null], 'Passwords must match')
  .required('Required'),