I am building an intermediate node server which acts as both socket client and server, I want to listen to backend server events and then forward the events to client(browser) after processing.

var socket = require('socket.io'),
    client = require('socket.io-client');

socket.on('event_name', function(data) {
    /* Logic to process response and relay to client */
    client.emit(this.event, data); // How can I get name of the outer event?
});

I want to get the event_name value in the callback. How can I do?

I am building an intermediate node server which acts as both socket client and server, I want to listen to backend server events and then forward the events to client(browser) after processing.

var socket = require('socket.io'),
    client = require('socket.io-client');

socket.on('event_name', function(data) {
    /* Logic to process response and relay to client */
    client.emit(this.event, data); // How can I get name of the outer event?
});

I want to get the event_name value in the callback. How can I do?

• javascript
• node.js
• sockets
• socket.io

3 Answers 3

I am not sure if you can get event name from the callback, but you can workaround it.

var socket = require('socket.io');

function registerEvent(eventName, cb) {
  socket.on(eventName, function () {
    var args = [].slice.apply(arguments);
    args.unshift(eventName);
    cb.apply(null, args);
  });
}

registerEvent('my_event', function (eventName, data) {
  // now you can access event name
  // it is prepended to arguments
  console.log('Event name', eventName);
});

You could try something similar :

// List of events relayed to client
const events = ['first_event', 'second_event', 'third_event'];

for (const event of events)
  socket.on(event, function(data) {
    console.log(event);     // You have access to the event name
    client.emit(e, data);   // Relay to client
  }); 
};

Since version 3.x, you can use middlewares, like this :

io.on("connection", socket => {
    socket.use(([event], next) => {
        socket.event = event;
        next();
    });
    socket.on("myevent", (data) => {
        console.log(socket.event); // Will print "myevent" in that case
    });
});