Yup is a JavaScript object schema validator and object parser. 

To check if the values of two fields are same or not using Yup, you can do:

Yup.object().shape({
   field1: Yup.string()
   .required('Required'),
   field2: Yup.string()
   .oneOf([Yup.ref('field1'), null], "Does not match with field1!")
   .required('Required')
});

For example, if you are validating password and repeat password it will be like:

Yup.object().shape({
   password: Yup.string()
   .required('Required'),
   confirmPassword: Yup.string()
   .oneOf([Yup.ref('password'), null], "Passwords don't match!")
   .required('Required')
});