custom-proptypes.js

Select.propTypes = {
    children: (props, propName, componentName) => {
        let error;
        const prop = props[propName];
        React.Children.forEach(prop, (child) => {
            // type.name seems to work for both Class and Functional components
            if (child.type.name !== 'Option') {
                error = new Error(`\`${componentName}\` only accepts children of type \`Option\`.`,);
            }
        });
        return error;
    },
};