isRequired

isRequired is pretty self explanatory. It determines that a value isn't valid if it's null, undefined or the empty string ''.

import { isRequired } from 'revalidate';

isRequired('My Field')();     // 'My Field is required'
isRequired('My Field')(null); // 'My Field is required'
isRequired('My Field')('');   // 'My Field is required'
isRequired('My Field')('42'); // undefined, therefore assume valid