Registering the map

AppMap is passed once at each end, createServer<AppMap> and browserClient<AppMap>, and is never inferred from contract. An application that builds clients or servers in many files can register the map once instead, and then drop the type argument everywhere:

import { Client, defineContract, type MapOf, reliable } from 'transport-io'

export const contract = defineContract({ chat: reliable<{ body: string }>() })
export interface AppMap extends MapOf<typeof contract> {}

declare module 'transport-io' {
  interface Register {
    map: AppMap
  }
}

// `Client` and `Server` now default to AppMap, with no type argument anywhere.
declare const client: Client
client.emit('chat', { body: 'hi' })

The tradeoff. It is a global augmentation, so there is one slot per process: two contracts in the same process conflict, and the type a file sees depends on which module was loaded rather than on what that file imported. It changes no hover; it removes the type argument and nothing else.

Leave the map unregistered and leave the type argument off, and you get the sentinel telling you to register a map or pass one.

@transport-io/react does not need it: createHooks<AppMap>() binds the hooks to a map the same way everything else takes one. Its named exports, useEvent, useCall and the rest, read the registered map instead.