JSFiddle - React, Tailwind, and code Playground

HTML

<textarea></textarea>
<textarea></textarea>
<textarea></textarea>
<a href="#" id="b" >Add Text</a>

JavaScript

document.getElementById("b").addEventListener("click", 


function(e) {
  e.preventDefault();
  var text='test',txtarea;
  
  var t = document.getElementsByTagName('textarea');
    for(var i =0 ;i<t.length;i++){
    if(t[i]==document.activeElement) {txtarea=t[i];console.log(txtarea)}
    }
  var scrollPos = txtarea.scrollTop;
  var strPos = 0;
  strPos = txtarea.selectionStart;
  var front = (txtarea.value).substring(0, strPos);
  var back = (txtarea.value).substring(strPos, txtarea.value.length);
  txtarea.value = front + text + back;
  strPos = strPos + text.length;
    txtarea.selectionStart = strPos;
    txtarea.selectionEnd = strPos;
    txtarea.focus();
  txtarea.scrollTop = scrollPos;
}
);