JSFiddle - React, Tailwind, and code Playground

HTML

<div class="form-group input select standort">
  <label class="control-label col-md-2" for="standort-id">Standort</label>
  <div class="col-md-6">
    <select name="standort_id" class="select2 form-control" id="standort-id">
      <option value="1" selected="selected">Erkrath</option>
    </select>
  </div>
</div>

<div class="form-group input select platz">
  <label class="control-label col-md-2" for="platz-id">Platz</label>
  <div class="col-md-6">
    <select name="platz_id" placeholder="--bitte wählen--" id="platz-id" class="form-control">
      <option value="1" selected="selected">Erkrath - Platz 1</option>
    </select>
  </div>
</div>

JavaScript

//$("#layout_select").children('option').hide();
$(function () {
  var showPlatz = function(selectedStandortId){
    $("#platz-id").children("option").hide();
    $("#platz-id").children("option").filter(function(){
      var platz = $(this).text();
      return platz.indexOf(selectedStandortId)!=-1;
    }).show();
    //set default value
    $('#platz-id option').each(function () {
        if ($(this).css('display') != 'none') {
            $(this).prop("selected", true);
            return false;
        }
    });
  };

  //set default standort
  var standort = $("#standort-id option:selected").text();
  showPlatz(standort.trim());
  $("#standort-id").change(function(){
	  var selected = $("#standort-id option:selected").text();
    showPlatz(selected.trim());
  });

});