var submit_button;
function emptyChk() {
 if ( !document.forms ) return;

 with ( document ) {
  var form = forms[ forms.length-1 ];
  for ( var i=0; i<form.length; i++ ) {
    submit_button = ( form.elements[i].type == 'submit' ) ? form.elements[i] : null;
  }
  if ( !submit_button ) return;
  submit_button.disabled = "disabled";

  form.onkeyup = function () {
   for ( var i=0; i<this.length; i++ ) {
    if ( this.elements[i].name.match( /name|pass|body/i ) && this.elements[i].value == '' ) {
     submit_button.disabled = "disabled";
     return;
    }
    submit_button.disabled = "";
   }
  }
  form.onmouseup = form.onkeyup;
 }
}

emptyChk();