/^(?:[\0-\uD7FF\uE000-\uFFFF]|[\uD800-\uDBFF](?![\uDC00-\uDFFF])|(?:[^\uD800-\uDBFF]|^)[\uDC00-\uDFFF])*$/

import non4byteCharsRegex from 'non-4byte-chars-regex';
 
non4byteCharsRegex.test('foo'); //=> true
non4byteCharsRegex.test('bar🍣baz'); //=> false
 
non4byteCharsRegex.test('吉'); //=> true
non4byteCharsRegex.test('𠮷'); //=> false