the server and client all work but 'on' and 'emit' not work, why?

[xiaofeilee]

server: socket.emit("test", "123456"); client: var socket = io.connect(SocketJS.connectUrl); //socket.on('connect', function(){ //alert('连接socket成功'); //});
socket.on('test', function(data){
alert('test ' + data); //not work why? });