<div class="wrap">
  <p class="texts">HELLO WORLD</p>
  <button class="btnCopy">copy</button>
</div>

  

.wrap {
  margin-bottom: 10px;
}

console.clear();


const btnCopy = document.querySelector('.btnCopy');

btnCopy.addEventListener('click', function() {
  const range = document.createRange();
  const texts = document.querySelector('.texts');
  range.selectNode(texts);
  
  const selection = window.getSelection();
  selection.removeAllRanges();
  selection.addRange(range);
  document.execCommand('copy');
  selection.removeAllRanges();
});