form-lib-9.md

const validate = values => { 
  /* returned object has all errors with name of field as key and error message as value */ 
  const errors = {}; 
  if (!values.userName) { 
    errors.userName = 'Please enter User Name'; 
  } // ... rest of conditions return errors; 
} 

const SampleForm = () => ( // ...sample form markup ); 

return reduxForm({ validate, ...otherValues })(SampleForm);