React props – set isRequired on a prop if another prop is null / empty

You don’t need another library, ‘prop-types’ provides this out of the box.
See https://facebook.github.io/react/docs/typechecking-with-proptypes.html

Example:

import PropTypes from 'prop-types';

//.......    

ExampleComponent.propTypes = {
    showDelete: PropTypes.bool,
    handleDelete: function(props, propName, componentName) {
        if ((props['showDelete'] == true && (props[propName] == undefined || typeof(props[propName]) != 'function'))) {
            return new Error('Please provide a handleDelete function!');
        }
    },

}