move-letters.ts

const getNextIndex = (currentIndex: number, array: any[]) =>
  currentIndex === array.length - 1 ? 0 : currentIndex + 1;

const getPreviousIndex = (currentIndex: number, array: any[]) =>
  currentIndex === 0 ? array.length - 1 : currentIndex - 1;

function moveLetters (input: string) {
  const sentence = input.split(' ');
  return sentence
    .map((currentWord, index) => {
      const nextWord = sentence[getNextIndex(index, sentence)];
      const previousWord = sentence[getPreviousIndex(index, sentence)];
      const strippedWord = currentWord.substr(1, currentWord.length - 2);
      return nextWord[0] + strippedWord + previousWord[previousWord.length - 1];
    });
}

console.log(moveLetters('bes le uoogit'));