Why writeln(); not producing a new line?

  <script type='text/javascript'> 
   //<![CDATA[
    for(var j = 0; j < 6;) {
     document.writeln(++j);
    }
   //]]>
   </script>
 

in the above code it suppose to give a new line if referring to the definition of the The writeln() method is identical to the write() method, with the addition of writing a newline character after each statement.

But in my case the output is 123456

---