<script type="text/javascript">
function ayir()
{
    var n ="" ;

    var gelen = document.getElementById('name1').value ;
    var l = gelen.length;

var i =0;
    for(i=l;i>=0;i--)
    {
        
        if((i % 4 ) == 0 )
        {
            n = n + " " + gelen.substr((l-i), 1) ;
        }else
        {
            n = n + gelen.substr((l-i), 1) ;
        }
    }
    


    
     document.getElementById('name').value = n ;

}

</script>


<form id="form1" name="form1" method="post" action="">
  <label>
  buraya yazin 
  <input type="text" name="name1" id="name1"   />

  <a href="javascript:ayir();">Tiklayin</a><br />

  farki burda gorun 
  </label>
  <input type="text" name="name" id="name"   />
</form>