<script type="text/javascript">
     Parse.initialize("xxxx", "xxxx");
     $("#post-form").submit(function(event){
         event.preventDefault();

      var uname = $("#uname").val();
      var pass = $("#pass").val();

      Parse.User.logIn(uname,pass, {
      success: function(user) {
      window.location="main.html";
      },
      error: function(user, error) {
      alert("Error: " + error.code + " " + error.message);
      } });});


      function checkLogin(){
      var currentUser = Parse.User.current();

      if (currentUser) {
      alert("Logged in as : "+currentUser.get("username"));
     window.location="www.abc.com/";

      } else {
      alert("Please Login");
      }}

     checkLogin();

     </script>

     </code>

<code>

     <script type="text/javascript">
     Parse.initialize("xxxx", "xxxx");

    function checkLogin(){
    var currentUser = Parse.User.current();

    if (currentUser) {
    alert("Logged in");

    } else {
    alert("Not logged in !");
    }}

     checkLogin();

       </script>
       </code>