koa js backend is showing error - DB not connected -how to fix this issue - koa

Question

I am also trying different network connections it returns the same error. Please help I am stuck last 15 days in this error. Oh! last one thing my laptop IP is dynamically changing so what can I do know.
this is my mongoose connecter
const mongoose = require('mongoose')
const connection = () =>{
const str = 'mongodb://localhost:27017/524'
mongoose.connect(str , () =>{
console.log("Connection is successfull")
} )
}
module.exports = {connection }
this is server js
const koa = require('koa')
const cors = require('koa-cors')
const bodyParser = require('koa-parser')
const json = require('koa-json')
const {connection} = require('./dal')
const userRouter = require('./Router/userRouter')
const app = new koa()
const PORT = 8000
app.use(cors())
app.use(bodyParser())
app.use(json())
app.use(userRouter.routes()).use(userRouter.allowedMethods())
app.listen(PORT, ()=>{
console.log(`Server is running on port ${PORT}`)
connection();
})
this is modle class
const mongoose = require('mongoose')
const Schema = mongoose.Schema
const UserSchema = new Schema ({
name:{
type:String,
required:true
},
email:{
type:String,
required:true,
unique:true
},
password:{
type:String,
required:true
},
role:{
type: Number,
default: 0
}
},{
timestamps:true
})
const User = mongoose.model('User', UserSchema)
module.exports = User
this is login route
const KoaRouter = require('koa-router')
const { register, login ,getAll } = require('../API/userAPI')
const userRouter = new KoaRouter({prefix: '/user'})
userRouter.post('/register', register)
userRouter.post('/login', login)
userRouter.get ('/get' , getAll)
module.exports = userRouter;
this is my contraller
const UserModel = require('../models/user.model')
const bcrypt = require('bcrypt')
const register = async (ctx) => {
try{
const user = ctx.request.body
const {name, email, password, role} = user
if (!name || !email || !password){
return (ctx.body = { message: "fill" });
}
else{
const exist = await UserModel.findOne({email})
if(exist){
return (ctx.body = { message: "User already exists" });
}else{
const salt = await bcrypt.genSalt();
const hashpassword = await bcrypt.hash(password, salt)
const newUser = new UserModel({
name,
email,
password : hashpassword,
role
})
await newUser.save()
return (ctx.body = { message: "User Registered" });
}
}
}catch(err){
console.log(err.message)
return (ctx.body = { message: err.message });
}
}
const login = async (ctx) => {
try{
const {email, password} = ctx.request.body
const user = await UserModel.findOne({email})
if (!user){
return ( ctx.body = {message:"User does not exist"})
}
else {
const isMatch = await bcrypt.compare(password, user.password)
if (!isMatch) {
return (ctx.body = { message:"Wrong Password"})
}else{
return (ctx.body = { user})
}
}
}catch(err){
return (ctx.body= {err})
}
}
const getAll = async (ctx) => {
try{
const users = await UserModel.find()
return (ctx.body = users)
}catch(err){
return (ctx.body= {err})
}
}
module.exports = {register, login ,getAll}
.
how to fix this.any ideas.Can any body guide me with this scenario.