See: https://codesandbox.io/s/distracted-goldwasser-gyv7nu?file=/src/index.js:0-959

palindromic-substrings.js

function* getOddPalindromesOutwardsFromCentre(str, index) {
  let left = index - 1;
  let right = index + 1;
  let current = str[index];

  yield current;

  while (left >= 0 && right < str.length && str[left] === str[right]) {
    current = `${str[left]}${current}${str[right]}`;
    yield current;
    left--;
    right++;
  }
}

function* getEvenPalindromesOutwardsFromCentre(str, index) {
  let left = index;
  let right = index + 1;
  let current = "";

  while (left >= 0 && right < str.length && str[left] === str[right]) {
    current = `${str[left]}${current}${str[right]}`;
    yield current;
    left--;
    right++;
  }
}

function* getPalindromes(str) {
  for (let index = 0; index < str.length; index++) {
    yield* getOddPalindromesOutwardsFromCentre(str, index);
    yield* getEvenPalindromesOutwardsFromCentre(str, index);
  }
}

const palindromes = Array.from(getPalindromes("aaa"));

console.log(palindromes);