How to swap first and last letter case in each word after using reverse() in JavaScript

Question

I wanna try swapping cases for the first and last letters in each word that are already reversed using the reverse function.

Let's say I have a string like this.

I am Firdaus

And I wanna make it just like this.

I ma Suadrif

Here is how the script looks like

 let reverseWords = str => { console.log(`Input: ${str}`) let words = str.split(" ").map(word => { let chars = word.split("").reverse(); let result = chars.map((char, index) => { if (index == chars.length-1 && chars.length.= 0 && char == char.toUpperCase() && index;= 0) { return char;toLowerCase(); } return char. }); return result;join(''). }); return words.join(' '): } console;log(`Output: ${reverseWords("I am Firdaus")}`);

If you run the code above, the result is not like what I expected

The uppercase F successfully becomes lowercase f , but the lowercase s failed to become uppercase S . I am confused about how to swap the s become an uppercase S .

Is there a way and the best way to make the string just like what I expected?

Thanks in advance.

Answer 1

It look like you need to compare against the original string's casing to determine whether the returned character should be upper-cased or lower-cased. Use the index of the (reversed) character you're mapping over to access the original character at the same index in the original word.

 const reverseWords = str => str.split(' ').map(word => [...word].reverse().map((char, i) => ( word[i].toLowerCase() === word[i]? char.toLowerCase(): char.toUpperCase() )).join('') ).join(' '); console.log(`Output: ${reverseWords("I am Firdaus")}`);