Javascript how to split newline

You should parse newlines regardless of the platform (operation system) This split is universal with regular expressions. You may consider using this:

var ks = $('#keywords').val().split(/\r?\n/);

E.g.

"a\nb\r\nc\r\nlala".split(/\r?\n/) // ["a", "b", "c", "lala"]

Try initializing the ks variable inside your submit function.

  (function($){
     $(document).ready(function(){
        $('#data').submit(function(e){
           var ks = $('#keywords').val().split("\n");
           e.preventDefault();
           alert(ks[0]);
           $.each(ks, function(k){
              alert(k);
           });
        });
     });
  })(jQuery);

It should be

yadayada.val.split(/\n/)

you're passing in a literal string to the split command, not a regex.