server.get('/_next/*', (req, reply) => - what it does

[heshamelmasry77]

Hey i see you have this

if (dev) {
        server.get('/_next/*', (req, reply) =>
            app.handleRequest(req.req, reply.res).then(() => {
              reply.sent = true;
            })
        );
      }

I would like to know what it does.

this is my server.js

const express = require("express")
const next = require("next")
const port = parseInt(process.env.PORT, 10) || 3000;

const dev = process.env.NODE_ENV !== "production"
const app = next({dev})
const handle = app.getRequestHandler()

app.prepare()
    .then(() => {
      const server = express();
      if (dev) {
        server.get('/_next/*', (req, reply) =>
            app.handleRequest(req.req, reply.res).then(() => {
              reply.sent = true;
            })
        );
      }
      server.get("/rooms/", (req, res) => {
        const actualPage = "/rooms";
        app.render(req, res, actualPage)
      });
      server.get("/rooms/:location", (req, res) => {
        const actualPage = "/rooms";
        const queryParams = {location: req.params.location};
        app.render(req, res, actualPage, queryParams)
      });

      server.get("/room/:id", (req, res) => {
        const actualPage = "/single-room"
        const queryParams = {id: req.params.id}
        app.render(req, res, actualPage, queryParams)
      });
      server.get("/post-room/:edit", (req, res) => {
        const actualPage = "/post-room"
        const queryParams = {id: req.params.id}
        app.render(req, res, actualPage, queryParams)
      });
      server.get("*", (req, res) => {
        return handle(req, res)
      });

      server.listen(port, err => {
        if (err) throw err;
        console.log(`> Ready on http://localhost:${port}`);
      });

      server.setNotFoundHandler((request, reply) =>
          app.render404(request.req, reply.res).then(() => {
            reply.sent = true;
          })
      );

      next();
    })
    .catch((ex) => {
      console.error(ex.stack)
      process.exit(1)
    })

thank you