我正在使用socket.io学习Node.js。在命令行中的基本聊天中，我想列出连接到服务器的套接字。
我的方法是在哈希图中存储几个套接字ID /用户名。当用户键入/ls时，它将向服务器发送一条消息，该消息将触发一个处理程序，该处理程序会将哈希图发送给用户，然后再显示。
客户端：
function chat_command(cmd, arg) {
switch (cmd) {
.
.
.
case 'ls':
socket.emit('send', {sender: nick ,action: 'list'});
break;
.
.
.
socket.on('message', function (data) {
.
.
.
// List all connected clients
else if(data.action === 'list'){
console.log(data.list, 'bug');
rl.prompt(true);
}
.
.
.
服务器端：
io.sockets.on('connection', function (socket) {
socket.on('send', function (data) {
if (data.type === 'notice') { //update the hasmap with the name
connectedSockets[socket.id] = data.nick;
// console.log(connectedSockets);
}
if (data.action === 'broadcast') {
io.sockets.emit('broadcast', data);
}
if (data.action === 'list') {
console.log(connectedSockets , 'ok')
socket.emit('message', {action:'list', list: connectedSockets});
}
else{
io.sockets.emit('message', data);
}
});
除了客户端首先将哈希图显示为未定义然后正确显示，而在socket.emit之前的console.log确认哈希图已定义并填充之外，它的工作原理很好。它返回以下内容：
> undefined bug
> { bjHo78hGv9QJbElQAAAB: 'hello' } bug
代替
> { bjHo78hGv9QJbElQAAAB: 'hello' } bug
一种快速的解决方法是替换
if (data.action === 'list')
作者
if (data.action === 'list'&& data.list !== undefined)
但是我仍然不明白它会先打印undefined然后再显示哈希图。当哈希映射从未从未被定义时，如何在不同的值上执行两次代码。这真让我烦恼！我缺少明显的东西吗？
任何见解将受到高度赞赏。谢谢。
编辑：这是一个console.trace，可能对某人有用。
Trace: undefined bug
at Socket.<anonymous> (/Users/soyanchardon/Documents/GitHub/iotProject/td1-Nanoboss/startercode/client side/client.js:87:17)
at Socket.Emitter.emit (/Users/soyanchardon/Documents/GitHub/iotProject/node_modules/component-emitter/index.js:133:20)
at Socket.onevent (/Users/soyanchardon/Documents/GitHub/iotProject/node_modules/socket.io-client/lib/socket.js:278:10)
at Socket.onpacket (/Users/soyanchardon/Documents/GitHub/iotProject/node_modules/socket.io-client/lib/socket.js:236:12)
at Manager.<anonymous> (/Users/soyanchardon/Documents/GitHub/iotProject/node_modules/component-bind/index.js:21:15)
at Manager.Emitter.emit (/Users/soyanchardon/Documents/GitHub/iotProject/node_modules/component-emitter/index.js:133:20)
at Manager.ondecoded (/Users/soyanchardon/Documents/GitHub/iotProject/node_modules/socket.io-client/lib/manager.js:345:8)
at Decoder.<anonymous> (/Users/soyanchardon/Documents/GitHub/iotProject/node_modules/component-bind/index.js:21:15)
at Decoder.Emitter.emit (/Users/soyanchardon/Documents/GitHub/iotProject/node_modules/component-emitter/index.js:133:20)
at Decoder.add (/Users/soyanchardon/Documents/GitHub/iotProject/node_modules/socket.io-parser/index.js:251:12)
Trace: { q6iF1NWEoiagjYwaAAAA: 'max', FudzkqUMYrrvp_u7AAAB: 'ben' } bug
at Socket.<anonymous> (/Users/soyanchardon/Documents/GitHub/iotProject/td1-Nanoboss/startercode/client side/client.js:87:17)
at Socket.Emitter.emit (/Users/soyanchardon/Documents/GitHub/iotProject/node_modules/component-emitter/index.js:133:20)
at Socket.onevent (/Users/soyanchardon/Documents/GitHub/iotProject/node_modules/socket.io-client/lib/socket.js:278:10)
at Socket.onpacket (/Users/soyanchardon/Documents/GitHub/iotProject/node_modules/socket.io-client/lib/socket.js:236:12)
at Manager.<anonymous> (/Users/soyanchardon/Documents/GitHub/iotProject/node_modules/component-bind/index.js:21:15)
at Manager.Emitter.emit (/Users/soyanchardon/Documents/GitHub/iotProject/node_modules/component-emitter/index.js:133:20)
at Manager.ondecoded (/Users/soyanchardon/Documents/GitHub/iotProject/node_modules/socket.io-client/lib/manager.js:345:8)
at Decoder.<anonymous> (/Users/soyanchardon/Documents/GitHub/iotProject/node_modules/component-bind/index.js:21:15)
at Decoder.Emitter.emit (/Users/soyanchardon/Documents/GitHub/iotProject/node_modules/component-emitter/index.js:133:20)
at Decoder.add (/Users/soyanchardon/Documents/GitHub/iotProject/node_modules/socket.io-parser/index.js:251:12)