如何在字符串中的重复单词前添加分隔符？

function addSeparatorToDuplicateWords(str, separator) {
  const words = str.split(' ');
  const uniqueWords = new Set();
  let result = '';

  for (let i = 0; i < words.length; i++) {
    const word = words[i];

    if (uniqueWords.has(word)) {
      result += separator + word;
    } else {
      result += ' ' + word;
      uniqueWords.add(word);
    }
  }

  return result.trim();
}

const inputString = 'This is a test test string with duplicate words test';
const separator = '***';
const resultString = addSeparatorToDuplicateWords(inputString, separator);
console.log(resultString);