JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://code.jquery.com/jquery-2.2.0.min.js"></script>
<input type="text" id="a">
<button type="button" id="sqrt">
  sqrt()
</button>

JavaScript

$('#sqrt').click(function() {
  var length = $('#a').val().length;
  $('#a').val($('#a').val() + 'sqrt()');
  $('#a').focus()[0].setSelectionRange(length+5, length+5);
});