How to use with Nuxt

This guide shows how to use Socket.IO within a Nuxt application.

Server​

Under the hood, Nuxt uses Nitro to handle the HTTP requests.

There are two steps to attach a Socket.IO server to a Nitro server:

Enable WebSockets​

WebSockets support in Nitro is currently experimental, so it needs to be manually enabled:

// https://nuxt.com/docs/api/configuration/nuxt-config

export default defineNuxtConfig({
  devtools: {
    enabled: true
  },
+ nitro: {
+   experimental: {
+     websocket: true
+   },
+ }
})

Reference: https://nitro.unjs.io/guide/websocket

Hook the Socket.IO server​

Our Socket.IO server is created in a Nitro plugin:

import type { NitroApp } from "nitropack";
import { Server as Engine } from "engine.io";
import { Server } from "socket.io";
import { defineEventHandler } from "h3";

export default defineNitroPlugin((nitroApp: NitroApp) => {
  const engine = new Engine();
  const io = new Server();

  io.bind(engine);

  io.on("connection", (socket) => {
    // ...
  });

  nitroApp.router.use("/socket.io/", defineEventHandler({
    handler(event) {
      engine.handleRequest(event.node.req, event.node.res);
      event._handled = true;
    },
    websocket: {
      open(peer) {
        const nodeContext = peer.ctx.node;
        const req = nodeContext.req;

        // @ts-expect-error private method
        engine.prepare(req);

        const rawSocket = nodeContext.req.socket;
        const websocket = nodeContext.ws;

        // @ts-expect-error private method
        engine.onWebSocket(req, rawSocket, websocket);
      }
    }
  }));
});

And voilà!

Client​

On the client side, all tips from our Vue 3 guide are valid.

The only difference is that you need to exclude the Socket.IO client from server-side rendering (SSR):

Structure:

├── components
│ ├── Connection.client.vue
│ └── socket.ts
...

import { io } from "socket.io-client";

export const socket = io();

<script setup>
import { socket } from "./socket";

const isConnected = ref(false);
const transport = ref("N/A");

if (socket.connected) {
  onConnect();
}

function onConnect() {
  isConnected.value = true;
  transport.value = socket.io.engine.transport.name;

  socket.io.engine.on("upgrade", (rawTransport) => {
    transport.value = rawTransport.name;
  });
}

function onDisconnect() {
  isConnected.value = false;
  transport.value = "N/A";
}

socket.on("connect", onConnect);
socket.on("disconnect", onDisconnect);

onBeforeUnmount(() => {
  socket.off("connect", onConnect);
  socket.off("disconnect", onDisconnect);
});

</script>

<template>
<div>
  <p>Status: {{ isConnected ? "connected" : "disconnected" }}</p>
  <p>Transport: {{ transport }}</p>
</div>
</template>

In the example above, the transport variable is the low-level transport used to establish the Socket.IO connection, which can be either:

• HTTP long-polling ("polling")
• WebSocket ("websocket")
• WebTransport ("webtransport")

If everything went well, you should see:

Status: connected
Transport: websocket

You can then exchange messages between the Socket.IO server and client with:

• socket.emit() to send messages

socket.emit("hello", "world");

• socket.on() to receive messages

socket.on("hello", (value) => {
  // ...
});

That's all folks, thanks for reading!

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