<script>
  function klik()
  {
    var a = document.getElementById("t1");
    var b = document.getElementById("c1");
    var b2 = document.getElementById("c2");
    var c = document.getElementById("t2");
    //
    if (b.checked)
    {
      c.value = a.value.toUpperCase();
      //Palindrom
      if (b2.checked)
      {
        var x = "";
        for (i=0; i<=c.value.length-1; i++)
        {
          x=c.value[i]+x;
        }
        c.value=x;
      }
    }
    else
    {
      c.value = a.value.toLowerCase();
      //Palindrom
      if (b2.checked)
      {
        var x = "";
        for (i=0; i<=c.value.length-1; i++)
        {
          x=c.value[i]+x;
        }
        c.value=x;
      }
    }
  }
</script>
<form style="margin: 100;">
  podaj tekst <input type="text" id="t1"><br>
  <input type="checkbox" id="c1"> Duże/małe litery<br>
  <input type="checkbox" id="c2"> Palindrom<br>
  wynik: <input type="text" id="t2"><br>
  <hr>
  <input type="button" value="Zamień" onclick="klik()">
</form>