const text = 'Образец text на русском языке';
const regex = /[u0400-u04FF]+/g;
const match = regex.exec(text);
console.log(match[0]); // logs 'Образец'
console.log(regex.lastIndex); // logs '7'
const match2 = regex.exec(text);
console.log(match2[0]); // logs 'на' [did not log 'text']
console.log(regex.lastIndex); // logs '15'
// and so on