JSFiddle - React, Tailwind, and code Playground

HTML

<div id="searchFields" class="control-group inlineForm">
  <form id="myForm">
    <div id="input1" style="margin-bottom:4px;" class="clonedInput">
      Regnr:
      <input type="text" name="regNr" placeholder="Regnr." id="name1" />
      <select>
        <option>ghhfgfgh</option>
        <option>ghhfgfgh</option>
        <option>ghhfgfgh</option>
        <option>ghhfgfgh</option>
      </select>

      PO.nr:
      <input type="text" id="poNr" placeholder="PO.nr." size="12" maxlength="12">
    </div>

    <div>
      <input type="button" id="btnAdd" value="add another Reg field" />
      <input type="button" id="btnDel" value="remove fields" />
    </div>
    <input type="button" value="GET INFO" class="last" id="getBaseInf">
  </form>
</div>

JavaScript

$('#btnAdd').click(function() {
  var num = $('.clonedInput').length; // how many "duplicatable" input fields we currently have
  var newNum = new Number(num + 1); // the numeric ID of the new input field being added

  // create the new element via clone(), and manipulate it's ID using newNum value  
  var newElem = $('#input' + num).clone().attr('id', 'input' + newNum);

  // manipulate the name/id values of the input inside the new element
  newElem.children(':first').attr('id', 'regNr' + newNum).attr('regNr', 'regNr' + newNum);

  // insert the new element after the last "duplicatable" input field
  $('#input' + num).after(newElem);

  // enable the "remove" button
  $('#btnDel').removeAttr('disabled');

  // business rule: you can only add 5 names
  if (newNum == 5)
    $('#btnAdd').attr('disabled', 'disabled');
});


$('#btnDel').click(function() {
  var num = $('.clonedInput').length;

  $('#input' + num).remove(); // remove the last element

  $('#btnAdd').attr('disabled', ''); // enable the "add" button

  // if only one element remains, disable the "remove" button
  if (num - 1 == 1)
    $('#btnDel').attr('disabled', 'disabled');
});

$('#btnDel').attr('disabled', 'disabled');