Express and Vue. With axios, req.body is not working

Question

Like i said in title. req.body don't work. I saw some examples and that use req.body(body-parser) well. But in my code, req.body is keep undefined. Also i found same problems and they said "app.use(bodyParser.json())" will work. But for me, no. So i ask how can i solve this error. Plz, help me.

This code is simple, Express and Vue login, signin test project. I think problem is in server file.

Server

var express = require("express");
var bodyParser = require("body-parser");
var path = require("path");
const mongoose = require("mongoose");

var index = require("./routes/index.js");
var login = require("./routes/login.js");
var signin = require("./routes/signin.js");

var app = express();
var http = require("http").Server(app);
mongoose.connect("mongodb://localhost:27017/test");

app.use('/', index);
app.use('/api/login', login);
app.use('/api/signin', signin);

app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: false }));
app.set("port", process.env.PORT || 3000);
app.use(express.static(path.join(__dirname, 'public')));

http.listen(app.get("port"), function() {
    console.log("server start in " + app.get("port"));
})

Router

const express = require("express");
const router = express.Router();
const User = require("../models/user.js");

router.post("/", function(req, res, next) {
    const id = req.body.id;
    const password = req.body.password;
    let info = {
        error: "false",
        words: "",
        id: "",
        password: ""
    }
    User.findOne({ id: id }, function(err, user) {
        if(err) {
            info.error = "true";
            info.words = "Unknown Error Come Out.";
            return res.send(info);
        }
        if(!user) {
            info.error = "true";
            info.words = "Please Check Your ID or Password";
            return res.send(info);
        }
        info.id = id;
        info.password = password;
        console.log(info);
        return res.send(info);
    })
});

module.exports = router;