<script type="text/javascript">
  function getQueryVariable(variable) {
    var query = window.location.search.substring(1);
    var vars = query.split('&');
    for (var i = 0; i < vars.length; i++) {
        var pair = vars[i].split('=');
        if (decodeURIComponent(pair[0]) == variable) {
            return decodeURIComponent(pair[1]);
        }
    }
 }

 var parcelNumber = getQueryVariable('parcelNumber');

 if(parcelNumber !== undefined) {
   document.getElementById('nr-przesylki').value = parcelNumber;
 }

</script>