[Wouter60]

You didn't describe the value of the $js variable, but in general, jQuery can handle elements by their id or class.
It should work if you do this:

PHP Code:

<?php echo form_input(array('id' => 'input1', 'name' => 'name', 'class' => 'form-control')); ?>
<?php echo form_input(array('id' => 'input2', 'name' => 'url', 'class' => 'form-control')); ?>

<script>
 $(document).ready(function() {
   $('#input1').keyup(function() {
       var text = $('#input1').val();
       $('#input2').val(text);
   });
 });
 </script>