socket.io-redis Typescript error

Question

I tried using @types/socket.io-redis like so:

import { Server as HttpServer } from 'http';
import socketIo, { Socket } from 'socket.io';
import redis, { RedisAdapter } from 'socket.io-redis';

export default function setupWebsocket(server: HttpServer) {
    const io = socketIo().listen(server);
    io.adapter(redis(process.env.REDIS_URL));

    const adapter: RedisAdapter = io.of('/').adapter;    // Error here
}

At the section where the Error here comment is, I got a red underline at the adapter variable with the error:

Type 'Adapter' is not assignable to type 'RedisAdapter'.

Property 'uid' is missing in type 'Adapter'.

Can anyone help me fix this issue? I'm quite new to Typescript

Answer 1

This is correct behaviour, type of io.of('/').adapter is Adapter. Fact that you assigned specific implementation(RedisAdapter) of interface(Adapter) don't change property type, as later you might change to different implementation of Adapter.

Possible solution might be to assign adapter directly after creation

import { Server as HttpServer } from 'http';
import socketIo, { Socket } from 'socket.io';
import redis, { RedisAdapter } from 'socket.io-redis';

export default function setupWebsocket(server: HttpServer) {
    const io = socketIo().listen(server);
    const adapter: RedisAdapter = redis(process.env.REDIS_URL);
    io.adapter(adapter);
    //... more code here
}

Other solution is to cast to desired type

const adapter: RedisAdapter = io.of('/').adapter as RedisAdapter;