data do not insert to mongodb, recieve empty json file

Question

i use code in app.js:

const express = require("express");
const app=express();
const _route=require('./router/router.js')
require('dotenv').config();
require('./Database/config.js');
const port_=process.env.PORT|| 8080;


app.use('/insert',async(req,res)=>{
    const newProduct=new product({
        name:'GLX SHAHIN 3',
        id:1,
        description:'Newest iranian phone'
    });
    try{
        await newProduct.save();
        res.send(`Inserted : ${newProduct}`);
    }
    catch(err){
        res.send(err);
    }
    });
app.listen(port_,'localhost',()=>{ console.log(`App run on port ${port_}`)});

and config the database as follow:

require('dotenv').config();
const mongoose=require('mongoose');
const port_=process.env.PORT|| 8080;
 const connectionString=`mongodb://localhost:${port_}:sale`;


mongoose.connect(connectionString,(err)=>{
    (err===true)? console.log('Fail to connect to mongodb'):console.log('Connect success.');
});

module.exports=mongoose;

i want insert to database. i enter localhost:3000/insert, get empty json file.The connection to the database appears to be established but data not insert to database. what is problem?