如何在没有数组或方法的字符串中查找最长的单词

function findLongestWord(str) {
  let longestWord = "";
  let longestLength = 0;
  let currentWord = "";
  let currentLength = 0;

  for (let i = 0; i <= str.length; i++) {
    if (str[i] === " " || i === str.length) {
      if (currentLength > longestLength) {
        longestWord = currentWord;
        longestLength = currentLength;
      }
      currentWord = "";
      currentLength = 0;
    } else {
      currentWord += str[i];
      currentLength++;
    }
  }

  return longestWord;
}

const inputString = "Hello world, this is a test";
const longestWord = findLongestWord(inputString);
console.log("The longest word is: " + longestWord);