Lowercase all letters in a string except the first letter and capitalize first letter of a string? - JavaScript

Question

I.e., if I have an input string:

input = 'hello World, whatS up?'

I want an output string to be:

desiredOutput = 'Hello World, whats up?'

If the first letter of any word in the string is already in upper case, leave it as is.

Answer 1

const upperCaseFirstLetter = string =>
 `${string.slice(0, 1).toUpperCase()}${string.slice(1)}`;

const lowerCaseAllWordsExceptFirstLetters = string =>
 string.replaceAll(/\S*/g, word =>
  `${word.slice(0, 1)}${word.slice(1).toLowerCase()}`
 );

const input = 'hello World, whatS up?';
const desiredOutput = upperCaseFirstLetter(lowerCaseAllWordsExceptFirstLetters(input));

console.log(desiredOutput);

Based on:

How do I make the first letter of a string uppercase in JavaScript?

and

How to capitalize first letter of each word, like a 2-word city?