JSFiddle - React, Tailwind, and code Playground

HTML

<form id="dataFields" action="save.php">
  <p>Feld 1 <input name="Feld1" type="text" size="30" maxlength="30"></p>
  <p>Feld 2 <input name="Feld2" type="text" size="30" maxlength="30"></p>
</form>
      <hr/>
      <button id="newField">neues Feld</button>
      <button id="eraseLast">letztes Feld löschen</button>

JavaScript

$('#newField').click(function(){
    var countField = $('#dataFields p').length;
    var newFNo = countField+1;
    var childrenCount = $('#dataFields').children.length;
    alert("children.length says "+childrenCount+" and length says "+countField);
    var htmlData = '<p>Feld '+newFNo+' <input name="Feld'+newFNo+'" type="text" size="30" maxlength="30"/></p>';
    $('#dataFields').append( htmlData);
});

$('#eraseLast').click(function(){
    $('#dataFields p:last-child').remove();
});