Node.JS why post is duplicated?

Question

JavaScript

Hello everyone, I made a chat, but for some reason, when sending messages, two messages are sent at once, and then three, four, five ...
What's the problem?
client

var socket = io();
    function sendMsg() {

      var $msg = $("#message");
      var $chat = $("#chat");
      socket.emit('sendMessage', $msg.val());

      socket.on('backMsg', function(data){
        $chat.append('<div class="well">'+data+'</div>');
      });
    }

server

socket.on('sendMessage', function(data){
    io.sockets.emit('backMsg', data);
  });

Answer 1

You hang up a handler every time you send socket.on('backMsg', function(data){
it. You only need to do it once.