jQuery Ajax函数错误

I have the following jquery function for an Ajax request:

function ajax_submit(){
    var submit_val= $('#login_form').serialize();
    dest = "login.php";
    $.ajax({
        type:"POST",
        url: dest,
        data: submit_val,
        success: function(data){
            if(data=='ok'){
                $("#spnmsg").fadeTo(200,0.1,function(){
                                $(this).removeClass().addClass('spn_success').html("Everything ok, logging you in...").fadeTo(900,1,function(){
                location.href="index.php";
                });
                });
            }else if(data=='ko'){
                $("#spnmsg").fadeTo(200,0.1,function(){
                $(this).removeClass().addClass('spn_error').html("Wrong Username or password. Please, try again").fadeTo(900,1);
                $("#txtUsername").focus();
                });
            }else if(data=='problemi'){
                $("#spnmsg").fadeTo(200,0.1,function(){
                $(this).removeClass().addClass('spn_error').html("Could not connect. Maybe system is down for maintenance. Please, try again later.").fadeTo(900,1);
                $("#txtUsername").focus();
                });
            }
        }
    });
};

The issue is that, even if login.php returns ok, ko or problemi and the variable data gets the right value it doesn't loop inside the if statement. What am I doing wrong so far? Can anyone find my error? Thanks a lot!

try by using trim()

if(data.trim()=='ok'){