[SOLVED] is new Router() and Router() identical in koa-router?

I saw the code that uses koa-router as below.

const Router = require('koa-router')

const routerWithoutNew = Router()

I thought it was an error, but I was surprised to see it working properly.

const Router = require('koa-router')

const routerWithNew = new Router()

and, it works fine, too.

what is difference between routerWithoutNew and routerWithNew?

They are treated identically due to the following line in the Koa Router source code:

if (!(this instanceof Router)) return new Router(opts);