document.getElementById('przyciskDodaj').addEventListener('click',function(){
  const nowyElement = document.getElementById('element').value.trim();
  if(nowyElement!==''){
    document.getElementById('komunikat').textContent='';
    document.getElementById('listaZadan').innerHTML += '<li>'+nowyElement+'</li>';
    document.getElementById('element').value='';
  } else {
    document.getElementById('komunikat').textContent='Uzupelnij pole';
  }
})