$("#loginBtn").click(function() {

$.ajax({

    type: 'POST',
    url: 'actions.php?action=login',
    data: 'username='+$("#loginUsername").val()+"&password="+$("#loginPassword").val(),
    success: function(result) {
            //futher processing
            }

});

});

quarkbits/
    |- actions.php
    |- js/
    |   |- main.js
    |- views/
    |    |- footer.php (contains the link to the main.js file)
    |    |- header.php (contains the login button
    |- index.php (includes footer.php file)