index.js

const express = require("express");
const userRouter = express.Router();
const groupRouter = express.Router();
const app = express();

userRouter.get("/user", (req, res) => res.end("user"));
groupRouter.get("/group", (req, res) => res.end("group"));

app.use("/api", userRouter);
app.use("/api", groupRouter);

app.listen(3000);