JSFiddle - React, Tailwind, and code Playground

JavaScript

function format(str){
  str = str.replace(/\b[a-z]/g, function(letter) {
    return letter.toUpperCase();
  });
  return str;
}

console.log(format("mark")); //Mark
console.log(format("mark o'loughlan")); //Mark O'Loughlan
console.log(format("mark's audi"));