Hello
In this code, $.ajax function worked , but success: function(html) does not work(document.getElementById).

I do not know why it does not work!? What do I do?

Code:
$(".submit").click(function(){    
        var entry_id = $("#entry_id").val();
        var comment_body = $("#comment_body").val();
        var comment_name = $("#comment_name").val();
        var comment_email = $("#comment_email").val();
        var comment_url = $("#comment_url").val();
        var dataString = 'entry_id=' + entry_id + '&comment_body=' + comment_body + '&comment_name=' + comment_name + '&comment_email=' + comment_email + '&comment_url=' + comment_url;
        
        if (comment_body == '' || comment_name == '' || comment_email == '' || comment_url == '') {
            alert('Please Give Valide Details');
        }
        else {
            $("#flash").show();
            $("#flash").fadeIn(400).html('<span class="loading">لطفا منتظر بمانید...</span>');
            $.ajax({
                type: "POST",
                url: "/zig-co/blog/comment_insert",
                data: dataString,
                cache: false,
                success: function(html){                                    
                    var s1 = document.getElementById('comment_body');
                    var s2 = document.getElementById('comment_name');
                    var s3 = document.getElementById('comment_email');
                    var s4 = document.getElementById('comment_url');
                    $("#update").append(html);
                    $("#update li:last").fadeIn("slow");
                      s1.value + s2.value + s3.value + s4.value;                  
                    $("#name").focus();
                    
                    $("#flash").hide();
                }
            });
        }
        return false;
    });