<script>
dec = 10;
bin = dec.toString(2);
document.write(bin);
</script>

<script>
  dec = 6;
  bin = "";
  while (dec>0)
  {
    if (dec%2==1) bin = "1"+bin;
    else bin = "0"+bin;
    dec = parseInt(dec/2);
  }
  document.write(bin);
</script>