JSFiddle - React, Tailwind, and code Playground

HTML

<select name="format" id="format" size="" class="validate['required'] form-control A" title="" style="" data-load-state="" data-tooltip="" data-cip-id="cIPJQ342845639">
<option value="99">offenes Format</option>
<option value="0">A0</option>
<option value="1">A1</option>
<option value="2">A2</option>
<option value="3">A3</option>
<option value="4" selected="selected">A4</option>
<option value="5">A5</option>
<option value="6">A6</option>
<option value="7">A7</option>
</select>

<input name="hoehe" id="hoehe" value="279" placeholder="" class="validate['required','digit'] form-control A" title="" style="" data-inputmask="" data-load-state="" data-tooltip="" type="text" data-cip-id="hoehe">
<input name="beite" id="breite" value="210" placeholder="" class="validate['required','digit'] form-control A" title="" style="" data-inputmask="" data-load-state="" data-tooltip="" type="text" data-cip-id="breite">

JavaScript

function format(){
  alert(jQuery('#format').val());
  switch(jQuery('#format').val()){
    case '0':
      alert('0');
      jQuery('#breite').val('840');  
      jQuery('#hoehe').val('1188');  
      break;
    case '1':
      jQuery('#breite').val('594');  
      jQuery('#hoehe').val('840');  
      break;
    case 2:
      jQuery('#breite').val('420');  
      jQuery('#hoehe').val('594');  
      break;
    case 3:
      jQuery('#breite').val('279');  
      jQuery('#hoehe').val('420');  
      break;
    case 4:
      jQuery('#breite').val('210');  
      jQuery('#hoehe').val('279');  
      break;
    case 5:
      jQuery('#breite').val('148');  
      jQuery('#hoehe').val('210');  
      break;
    case 6:
      jQuery('#breite').val('105');  
      jQuery('#hoehe').val('148');  
      break;
    case 7:
      jQuery('#breite').val('74');  
      jQuery('#hoehe').val('105');  
      break;
    default:
      jQuery('#breite').val('210');  
      jQuery('#hoehe').val('279');  
      break;
  }
}

jQuery(document).ready(function(){
  jQuery('#format').change(format);
});