Can't get value of req.cookies in router function of Express

Question

I have a file router.js of Express like this:

const router = require("express").Router();
router.get("/getcookie", (req, res) => {
        console.log(req.cookies) //I get null of object in console log here
    })
module.exports = router;

And in file index.js of Express app:

const express = require("express");
var cookieParser = require('cookie-parser');
const routerCookie = require("./router.js")
const app = express();
...
app.use(cookieParser())
app.use("/api", routerCookie)
app.listen(5000)

When run this i receive a null of Object from console.log(req.cookies) in log.

But it work without use require("express").Router() like this:

const express = require("express");
var cookieParser = require('cookie-parser');
const routerCookie = require("./router.js")
const app = express();
...
app.use(cookieParser())
app.use("/apicookies", (req, res) => {
  console.log(req.cookies) //I receive cookies in here
})
app.listen(5000)

My question is how i can get value of req.cookies through the require("express").Router() ?