Why is $(document).ready(); undefined?

I thought that I was doing everything right, however I keep getting this error. $(document).ready(); // undefined in the console. I imported my jquery script.

    <script src = "//ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
    <script >

        $(document).ready(function(){

            $("div#chat").hide();

        });

        function send_file(){

        }

        function remove_selected(){

        }

        function changeToFile(){

        }

        function chatToProfile(){

        }

        function changeToChat(){

        }
    </script>