Bagaimana cara menambah number format di bagian input harga

 <input type="text" id="txt1"  onkeyup="sum();" /> //input Jumlah, disininya otomatis jadi number format ga lagi 100000, tapi jadi 100.000
<input type="text" id="txt2"  onkeyup="sum();" />= Total Hari
<input type="text" id="txt3"/>

<script>
function sum() {
      var txtFirstNumberValue = document.getElementById('txt1').value;
      var txtSecondNumberValue = document.getElementById('txt2').value;
      var result = parseInt(txtFirstNumberValue) / parseInt(txtSecondNumberValue); /pembagian
      if (!isNaN(result)) {
         document.getElementById('txt3').value = result;
      }
}
function rupiah($txt1){

	$hasil_rupiah = "Rp " . number_format($txt1,2,',','.');
	return $hasil_rupiah;

}
</script>