Adds Router.expand which accepts and expands Router instances for Router.use.

koa-router-expand.js

'use strict'
const { flatten } = require('lodash')
const Router = require('koa-router')

/**
 * Adds Router.expand which accepts and expands Router instances for Router.use.
 * @returns this
 */

Router.prototype.expand = function (...args) {
  return this.use(
    ...flatten(
      args.map(
        mw => mw instanceof Router
          ? [mw.routes(), mw.allowedMethods()]
          : mw
      )
    )
  )
}

/**
 * @example
 * const Router = require('koa-router')
 * const router = new Router()
 * const subRouter = new Router()
 * subRouter.get(...)
 * subRouter.post(...)
 * router.use(subRouter)
 */