How to find a word in a div block and give it a class, using JS, which is written in capital LETTERS?

Question

JavaScript

How to find a word in a div block and give it a class, using JS, which is written in capital LETTERS?

for example

<div class="block">
  <h1>СЛОВО большими буквами</h1>
</div>

Answer 1

How to find a word in a div and give it a class...

What does it mean to assign a class to a word? No, seriously - do you understand what you said?
You can wrap the found word in a span with the desired class :

block.innerHTML = block.innerHTML.replace(/([А-Я]+)/g, '<span class="здесь-ваш-класс">$1</span>');