1function copyToClipboard(value) {
2  navigator.clipboard.writeText(value)
3}

1var copyTextareaBtn = document.querySelector('.js-textareacopybtn');
2
3copyTextareaBtn.addEventListener('click', function(event) {
4  var copyTextarea = document.querySelector('.js-copytextarea');
5  copyTextarea.focus();
6  copyTextarea.select();
7
8  try {
9    var successful = document.execCommand('copy');
10    var msg = successful ? 'successful' : 'unsuccessful';
11    console.log('Copying text command was ' + msg);
12  } catch (err) {
13    console.log('Oops, unable to copy');
14  }
15});
16
17////html code below
18<p>
19  <button class="js-textareacopybtn" style="vertical-align:top;">Copy Textarea</button>
20  <textarea class="js-copytextarea">Hello I'm some text</textarea>
21</p>