telegraf/src/middleware.ts

Modern Telegram Bot Framework

import { Context } from './context'

/*
  next's parameter is in a contravariant position, and thus, trying to type it
  prevents assigning `MiddlewareFn<ContextMessageUpdate>`
  to `MiddlewareFn<CustomContext>`.
  Middleware passing the parameter should be a separate type instead.
*/
export type MiddlewareFn<C extends Context> = (
  ctx: C,
  next: () => Promise<void>
  // eslint-disable-next-line @typescript-eslint/no-invalid-void-type
) => Promise<unknown> | void

export interface MiddlewareObj<C extends Context> {
  middleware: () => MiddlewareFn<C>
}

export type Middleware<C extends Context> = MiddlewareFn<C> | MiddlewareObj<C>