为啥用ajax传值后画面还是刷新呢

为什么用ajax传值后画面还是刷新呢

JScript code

$("#send").click(function() {                            var msg = $("#msg").val();                            var user;                            if($("#user").val()==""){                                user="游客";                            }else{                                user = $("#user").val();                            }                            $.ajax({                                type : "post",                                url : "chat_add",                                data : {                                    msg : msg,                                    user : user                                },                                dataType : "json",                                success : function(jsonStr) {                                                                    var data = eval(jsonStr);                                    $                                            .each(                                                    data,                                                    function(i,                                                            n) {                                                        msgchat += n.time                                                        + "&nbsp;"                                                        + n.user                                                        + "&#58"                                                        + "<br>"                                                        + "&nbsp;&nbsp;&nbsp;&nbsp;"                                                        + n.msg                                                        + "<br>";                                                    });                                    document                                            .getElementById('showMsg').innerHTML = msgchat;                                    document                                            .getElementById('showMsg').scrollTop = document                                            .getElementById('showMsg').scrollHeight;                                }                            });                            $("#msg").val("");//清空                        });

Java code

    public String add() throws Exception  {        chat.setMsg(msg);        chat.setUser(user);        this.chatService.addMsg(chat);        this.msglist=this.chatService.searchMsg(chat);//查询        outputJson(msglist);        return null;    }

JScript code

$("#msg").val("");//清空return false;///////////增加这句阻止表单提交