Class Rule

This formats the formatter string and includes the variables in it from values object. The variable key must be surrounded by % char.

const formattedString = formatMessage('%name% should not be empty.', { name: 'Email' });
// Returns 'Email should not be empty.'

// If the message contains actual `%` symbol, it should be prefixed with `-`.
const formattedString = formatMessage('%name% should be greater than 90-%.',
 { name: 'Marks' }
);
// Returns 'Marks should be greater than 90%.'

Validate the value and return the error string if there are any otherwise return undefined.