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我已经实现了一个简单的聊天应用程序。但是当客户端离开页面或关闭浏览器选项卡时，断开连接事件被多次调用。有时两次有时三次。在断开回调函数内部，我将聊天记录插入数据库。由于回调函数多次调用相同的聊天记录，因此多次插入。不知道是什么问题。请帮忙。

代码是这样的

服务器端代码

var sys = require('sys');
var fs = require('fs');
var io = require('socket.io');
var connection = function(){
sys.puts("Here")
var mysql = require('mysql');
var sql = mysql.createConnection({
host:'localhost',
port:3306,
user:'root',
password:'root'
});
sql.query('use chat');
sys.puts("Here" +sql)
return sql;
}
var Server = require('http').createServer(function(req, response){

sys.puts("request recieved");
response.writeHeader(200,{"Content-Type":"text/html"});
response.write("Hello World");
var rs = fs.createReadStream(__dirname + '/chat.html')
sys.pump(rs,response);
});

var history = "";
var socket = io.listen(Server);

var mysql = connection();
socket.sockets.on('connection',function(client){
sys.puts("socket connected ID "+client.id);
sys.puts("session id",client.handshake.sessionID)
var username;
client.send('Welcome to chat');
client.send('Enter your name');
client.on('message',function(message){
if(!username)
{
username = message;
client.send('Welcome,' +username);
return;
}
feedback = username+' sent:'+message;
history = history + feedback + '\n';
client.send(feedback)
client.broadcast.send(feedback); 
sys.puts("History is " +history);
sys.puts("mysql" +mysql);

 client.on('disconnect',function(){
      mysql.query('insert into tblchatHistory (fldChatHistory) values ("'+history+'")',function(err){
     sys.puts("error" +err);
     history = "";
 })
  sys.puts("socket connected ID "+client.id);
 })
})
})
Server.listen(4000);

客户端代码

    <script type="text/javascript">
        var socket;
        socket = new io.connect("http://localhost:4000");
        var connect = false;
        socket.on('connect',function(){
            alert("connected "+socket.socket.sessionid);
            connect = true;
        })
        function chat()
        {
         socket.on('message',function(message){
            var data = message;
            var list ='<li>' +data +'</li>'

            document.getElementById("log").innerHTML +=list;
            })

        }
        function sendMsg(event)
         { 
             var entry = document.getElementById("entry");
               var msg = entry.value;
                if(event.keyCode != 13)return
                if(msg)
                    {
                       if(connect)
                           {
                             socket.emit('message',msg);
                             entry.value = "";  
                           }
                     }
         }
   </script>

<body onload="chat();">
    <h1>Chat</h1>
    <div><ul id="log"></ul></div>
    <div id="console">
        <input type="text" id="entry" onkeypress="sendMsg(event);"/>
    </div>
    <div><a href="http://localhost:8085/BillDesk/welcomeJSF.jsf" >Exit chat</a></div>
</body>
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