patternjavascriptMinor

Creating chat commands properly with Socket.IO

Submitted by: @import:stackexchange-codereview·Mar 10, 2026·

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chatcreatingproperlywithcommandssocket

Problem

I am developing a chat program (mountreus-chat and GitHub) in Node.js using Socket.io and my code looks awful. I'm starting to use commands and now it's even worse.

Here's a code snippet (you can find every detail on the Github repo):

io.on('connection', function(socket){
      if(socketConnections().length  BROADCAST: ' + finalMessage + '' + messageDate + '';
            }else if(firstWord === "/bot-say"){
                var finalMessage = markedMessage.substr(markedMessage.indexOf(" ") + 1);
                var messageToBeSent = ' Chat bot: ' + finalMessage + '' + messageDate + '';
            }else{
            var messageToBeSent = '' + escapeHTML(msg.username) + ': ' + markedMessage + '' + messageDate + '';
            }
            if(messageToBeSent.length Available commands:/help - Display help commands/bot-say <message> - Give something for the bot to say!/broadcast <message> - Broadcast a message');
            }
        });
      socket.on('users', function(){
                var socketsConnected = socketConnections(socket.handshake.query.room, "/");
                io.to(socket.handshake.query.room).emit('connections', socketsConnected.length + 1);
                });
      socket.on('disconnect', function(){
                var socketsConnected = socketConnections(socket.handshake.query.room, "/");
                io.to(socket.handshake.query.room).emit('connections', socketsConnected.length + 1);
                });
      }else{
      socket.emit('chat message', 'PM: Sorry, we cannot allow more than 1024 connections in the server');
      socket.emit('chat message', 'PM: Disconnecting! Try again later.');
      socket.emit('connections', 'You are not connected.');
      socket.disconnect();
      }
      });

Solution

You can gain a lot of readability by formatting the code (every decent editor will do a passable job at this with a single keystroke) and extracting several small functions (refactoring). I'll start with this but only extract the reusable functions.

Note: I assumed you can emit the initial connection count after binding the commands. If not, move the first call to emitConnectionCount inside setupSocket.

io.on('connection', function (socket) {
    if (socketConnections().length Available commands:/help - Display help commands/bot-say <message> - Give something for the bot to say!/broadcast <message> - Broadcast a message');
        } else if (firstWord === "/broadcast") {
            finalMessage = markedMessage.substr(markedMessage.indexOf(" ") + 1);
            messageToBeSent = ' BROADCAST: ' + finalMessage + '' + messageDate + '';
        } else if (firstWord === "/bot-say") {
            finalMessage = markedMessage.substr(markedMessage.indexOf(" ") + 1);
            messageToBeSent = ' Chat bot: ' + finalMessage + '' + messageDate + '';
        } else {
            messageToBeSent = '' + escapeHTML(msg.username) + ': ' + markedMessage + '' + messageDate + '';
        }
        if (messageToBeSent.length <= 8192) {
            if (!verifyEmptyness(msg.message)) {
                emitToRoom(messageToBeSent);
            } else {
                emitToUser('PM: Sorry, you cannot send empty messages.');
            }
        } else {
            emitToUser('PM: Oops! You cannot send messages longer than 8192 characters. Sorry!');
        }
    }

    function emitToRoom(message, command) {
        io.to(socket.handshake.query.room).emit(command || 'chat message', message);
    }

    function emitToUser(message, command) {
        socket.emit(command || 'chat message', message);
    }

    function emitConnectionCount() {
        var socketsConnected = socketConnections(socket.handshake.query.room, "/");
        emitToRoom(socketsConnected.length + 1, 'connections');
    }
});

That's much easier to grok already, but let's tackle that complicated handleMessage function next. What are its responsibilities?

Parse the message to extract an optional command (/help, /broadcast, and /bot-say).

Handle the help command.

Fail if the message is empty.

Format the message using Markdown.

Embed it into an HTML snippet.

Fail if the formatted message is too long.

Emit the formatted message.

Wow, that's a lot of work--too much for a single function. Let's simplify it by extracting functions for emitting the help text and formatting the message.

function handleMessage(chat) {
    var message = chat.message;
    if (message === "/help") {
        handleHelp();
    } else {
        var split = message.indexOf(" ");
        var command;
        if (split === -1) {
            command = '/chat';
        } else {
            command = message.substr(0, split);
            message = message.substr(split);
        }
        if (verifyEmptyness(message)) {
            emitToUser('PM: Sorry, you cannot send empty messages.');
        } else {
            var realMessage = formatMessage(command, message, chat.username, moment(chat.date).format("LT, D/M"));
            if (realMessage.length > 8192) {
                emitToUser('PM: Oops! You cannot send messages longer than 8192 characters. Sorry!');
            } else {
                emitToRoom(realMessage);
            }
        }
    }
}

function formatMessage(command, message, user, date) {
    var intro;
    switch (command) {
        case '/broadcast':
            intro = 'BROADCAST';
            break;
        case '/bot-say':
            intro = 'Chat bot';
            break;
        case '/chat':
            intro = escapeHTML(user);
            break;
        default:
            intro = 'UNKNOWN COMMAND';
            message = command;
            break;
    }
    return ' ' + intro + ': ' + message + '' + date + '';
}

function handleHelp() {
    sendToUser(
        'Montreus Chat - v1.3.3'
        + 'Available commands:'
        + '/help - Display help commands'
        + '/bot-say <message> - Give something for the bot to say!'
        + '/broadcast <message> - Broadcast a message'
    );
}

That's better, but handleMessage is still doing too much. I don't like that it has to parse the original message, check for an empty chat message, and send the formatted message if it's not too long. Let's extract the parsing first.

```
function handleMessage(chat) {
if (chat.message === '/help') {
handleHelp();
} else {
var parsed = parseMessage(chat.message);
if (verifyEmptyness(parsed.message)) {
emitToUser('PM: Sorry, you cannot send empty messages.');
} else {
var message = formatMessage(parsed.command, parsed.message, chat.username, moment(chat.date).format("LT, D/M"));
if (message.length > 8192) {
emitToUser('PM: Oops! You

Code Snippets

io.on('connection', function (socket) {
    if (socketConnections().length <= 1024) {
        setupSocket();
        emitConnectionCount();
    } else {
        disconnect();
    }

    function setupSocket() {
        socket.username = socket.handshake.query.username;
        socket.toString = function () {
            return this.name
        };
        socket.join(socket.handshake.query.room);
        socket.on('postName', handleUsername);
        socket.on('chat message', handleMessage);
        socket.on('users', emitConnectionCount);
        socket.on('disconnect', emitConnectionCount);
    }

    function disconnect() {
        emitToUser('PM: Sorry, we cannot allow more than 1024 connections in the server');
        emitToUser('PM: Disconnecting! Try again later.');
        emitToUser('You are not connected.', 'connections');
        socket.disconnect();
    }

    function handleUsername(username) {
        socket.username = username;
    }

    function handleMessage(msg) {
        var markedMessage = markdown.renderInline(msg.message);
        var messageDate = moment(msg.date).format("LT, D/M");
        var firstWord = markedMessage.substr(0, markedMessage.indexOf(" "));
        var messageToBeSent;
        var finalMessage;
        if (msg.message === "/help") {
            emitToUser('Montreus Chat - v1.3.3<br>Available commands:<br>/help - Display help commands<br>/bot-say &lt;message&gt; - Give something for the bot to say!<br>/broadcast &lt;message&gt; - Broadcast a message');
        } else if (firstWord === "/broadcast") {
            finalMessage = markedMessage.substr(markedMessage.indexOf(" ") + 1);
            messageToBeSent = '<p class="alignLeft"> BROADCAST: ' + finalMessage + '</p><p class="alignRight">' + messageDate + '</p>';
        } else if (firstWord === "/bot-say") {
            finalMessage = markedMessage.substr(markedMessage.indexOf(" ") + 1);
            messageToBeSent = '<p class="alignLeft"> Chat bot: ' + finalMessage + '</p><p class="alignRight">' + messageDate + '</p>';
        } else {
            messageToBeSent = '<p class="alignLeft">' + escapeHTML(msg.username) + ': ' + markedMessage + '</p><p class="alignRight">' + messageDate + '</p>';
        }
        if (messageToBeSent.length <= 8192) {
            if (!verifyEmptyness(msg.message)) {
                emitToRoom(messageToBeSent);
            } else {
                emitToUser('PM: Sorry, you cannot send empty messages.');
            }
        } else {
            emitToUser('PM: Oops! You cannot send messages longer than 8192 characters. Sorry!');
        }
    }

    function emitToRoom(message, command) {
        io.to(socket.handshake.query.room).emit(command || 'chat message', message);
    }

    function emitToUser(message, command) {
        socket.emit(command || 'chat message', message);
    }

    function emitConnectionCount() {
        var socketsConnected = socketConnections(socket.handshake.query.room, "/");
        emitToRoom(s

function handleMessage(chat) {
    var message = chat.message;
    if (message === "/help") {
        handleHelp();
    } else {
        var split = message.indexOf(" ");
        var command;
        if (split === -1) {
            command = '/chat';
        } else {
            command = message.substr(0, split);
            message = message.substr(split);
        }
        if (verifyEmptyness(message)) {
            emitToUser('PM: Sorry, you cannot send empty messages.');
        } else {
            var realMessage = formatMessage(command, message, chat.username, moment(chat.date).format("LT, D/M"));
            if (realMessage.length > 8192) {
                emitToUser('PM: Oops! You cannot send messages longer than 8192 characters. Sorry!');
            } else {
                emitToRoom(realMessage);
            }
        }
    }
}

function formatMessage(command, message, user, date) {
    var intro;
    switch (command) {
        case '/broadcast':
            intro = 'BROADCAST';
            break;
        case '/bot-say':
            intro = 'Chat bot';
            break;
        case '/chat':
            intro = escapeHTML(user);
            break;
        default:
            intro = 'UNKNOWN COMMAND';
            message = command;
            break;
    }
    return '<p class="alignLeft"> ' + intro + ': ' + message + '</p><p class="alignRight">' + date + '</p>';
}

function handleHelp() {
    sendToUser(
        'Montreus Chat - v1.3.3'
        + '<br>Available commands:'
        + '<br>/help - Display help commands'
        + '<br>/bot-say &lt;message&gt; - Give something for the bot to say!'
        + '<br>/broadcast &lt;message&gt; - Broadcast a message'
    );
}

function handleMessage(chat) {
    if (chat.message === '/help') {
        handleHelp();
    } else {
        var parsed = parseMessage(chat.message);
        if (verifyEmptyness(parsed.message)) {
            emitToUser('PM: Sorry, you cannot send empty messages.');
        } else {
            var message = formatMessage(parsed.command, parsed.message, chat.username, moment(chat.date).format("LT, D/M"));
            if (message.length > 8192) {
                emitToUser('PM: Oops! You cannot send messages longer than 8192 characters. Sorry!');
            } else {
                emitToRoom(chat, command, message);
            }
        }
    }
}

function parseMessage(message) {
    var split = message.indexOf(' ');
    if (split === -1 || message.charAt(0) !== '/') {
        return {command: '/chat', message: message};
    } else {
        return {command: message.substr(0, split), message: message.substr(split)};
    }
}

function handleMessage(chat) {
    if (chat.message === '/help') {
        handleHelp();
    } else {
        handleChat(chat);
    }
}

function handleChat(chat) {
    var parsed = parseMessage(chat.message);
    var formatted = formatMessage(parsed.command, parsed.message, chat.username, moment(chat.date).format("LT, D/M"));
    if (verifyEmptyness(parsed.message)) {
        emitToUser('PM: Sorry, you cannot send empty messages.');
    } else if (formatted.length > 8192) {
        emitToUser('PM: Oops! You cannot send messages longer than 8192 characters. Sorry!');
    } else {
        emitToRoom(chat, command, formatted);
    }
}

io.on('connection', function (socket) {
    if (socketConnections().length > 1024) {
        disconnect();
    } else {
        setupSocket();
        emitConnectionCount();
    }

    function disconnect() {
        emitToUser('PM: Sorry, we cannot allow more than 1024 connections in the server');
        emitToUser('PM: Disconnecting! Try again later.');
        emitToUser('You are not connected.', 'connections');
        socket.disconnect();
    }

    function setupSocket() {
        socket.username = socket.handshake.query.username;
        socket.toString = function () {
            return this.name
        };
        socket.join(socket.handshake.query.room);
        socket.on('postName', handleUsername);
        socket.on('chat message', handleMessage);
        socket.on('users', emitConnectionCount);
        socket.on('disconnect', emitConnectionCount);
    }

    function handleUsername(username) {
        socket.username = username;
    }

    function handleMessage(chat) {
        if (chat.message === '/help') {
            handleHelp();
        } else {
            handleChat(chat);
        }
    }

    function handleHelp() {
        sendToUser(
            'Montreus Chat - v1.3.3'
            + '<br>Available commands:'
            + '<br>/help - Display help commands'
            + '<br>/bot-say &lt;message&gt; - Give something for the bot to say!'
            + '<br>/broadcast &lt;message&gt; - Broadcast a message'
        );
    }

    function handleChat(chat) {
        var parsed = parseMessage(chat.message);
        var formatted = formatMessage(parsed.command, parsed.message, chat.username, moment(chat.date).format("LT, D/M"));
        if (verifyEmptyness(parsed.message)) {
            emitToUser('PM: Sorry, you cannot send empty messages.');
        } else if (formatted.length > 8192) {
            emitToUser('PM: Oops! You cannot send messages longer than 8192 characters. Sorry!');
        } else {
            emitToRoom(chat, command, formatted);
        }
    }

    function parseMessage(message) {
        var split = message.indexOf(' ');
        if (split === -1 || message.charAt(0) !== '/') {
            return {command: '/chat', message: message};
        } else {
            return {command: message.substr(0, split), message: message.substr(split)};
        }
    }

    function formatMessage(command, message, user, date) {
        var intro;
        switch (command) {
            case '/broadcast':
                intro = 'BROADCAST';
                break;
            case '/bot-say':
                intro = 'Chat bot';
                break;
            case '/chat':
                intro = escapeHTML(user);
                break;
            default:
                intro = 'UNKNOWN COMMAND';
                message = command;
                break;
        }
        return '<p class="alignLeft"> ' + intro + ': ' + message + '</p><p class="alignRight">' + date + '</p>';
    }

    function emitConnectionCount() {

Context

StackExchange Code Review Q#78552, answer score: 5

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