It's better of course to extract the environment variables, but for the sake of clarity, they're taken from
process.envon-demand.
Setup pusher client (for client components):
// lib/pusher/client.ts
import Pusher from 'pusher-js'
const key = process.env.NEXT_PUBLIC_PUSHER_APP_KEY
const cluster = process.env.NEXT_PUBLIC_PUSHER_CLUSTER