JSFiddle - React, Tailwind, and code Playground

HTML

<button id="js-add-question-row">Add Notes</button>
<form action="" method="" id="someform">
    <textarea name="quiz[content][0]"></textarea>
</form>

JavaScript

$(document).ready(function() {
      $("#js-add-question-row").click(function() {
        addQuestion();
      });
    });

    function addQuestion() {
      var question = $("textarea:last").clone();
      question = updateQuestion(question);
      question.insertAfter("textarea:last");
    }

    // This part substitutes out the index number and then increments the last by one
    function updateQuestion(question) {
      var old_name = question.attr("name");
      var result = /\[[\d]+\]/.exec(old_name).toString();
      var old_index = result.slice(1, -1);
      var new_index = (parseInt(old_index, 10) + 1).toString();
      var new_name = old_name.replace(old_index, new_index);
      question.attr("name", new_name);
      return question
    }