使用 javascript 交换字符串中每个单词的第一个和最后一个字母

Question

Given a string of words separated by spaces, write a function that swaps the first and last letters of every word. You may assume that every word contains at least one letter, and that the string will always contain at least one word. You may also assume that each string contains nothing but words and spaces, and that there are no leading, trailing, or repeated spaces.

This is what I have so far

function first_last(str1){
 if (str1.length <= 1) {
  return str1;
 }

  mid_char = str1.substring(1, str1.length - 1);
  return (str1.charAt(str1.length - 1)) + mid_char + str1.charAt(0);
 }
 console.log(first_last('Hello there')); //eello therH

Answer 1

first split the sentence to word and then swap the first and last letter

 const str = "This is a hello world string"; const result = str.split(" ").map(word => { const len = word.length; if (len > 1) { word = word[len-1] + word.substring(1, len-1) + word[0]; } return word; }).join(" "); console.log(result)

breaking it into statements for people who find the implementation difficult to comprehend

const str = "This is a hello world string";

const arr = str.split(" ");

const swapWords = arr.map(word => {
  const len = word.length;
  if (len > 1) {
    word = word[len - 1] + word.substring(1, len - 1) + word[0];
  }
  return word;
});

const result = swapWords.join(" ");

console.log(result)

Answer 2

A bit fancier example with ES6 stuff:

 const invertFirstWithLastLetter = string => string.split(" ").map(word => { if (word.length === 1) { return word; }; word = [...word]; [word[0], word[word.length - 1]] = [word[word.length - 1], word[0]]; return word.join("").toString(); }).join(" "); console.log(invertFirstWithLastLetter("ES6 is not a crime"));

How it works:

We split the string on every space, creating an array of words. We map the array:

if the word is composed of a single letter/char only, we don't need to invert.

If it's bigger than one character, we will spread the array literal , hence we will create another (nested) array and we are going to invert the first and last letter. Before returning this (nested) array, we join it again (to remove , ) and we return a string out of it instead of a (nested) array.

In the end, we are left with an array with the words (with inverted first and last letter), that we will merge again, recreating the same space that we used to split at the first line of the function.

Is this the best approach (the most performant way) to do that? Probably not. But it might teach a lot of cool stuff.