How to resolve this error??? during mongodb connection?

const mongoClient=require('mongodb').mongoClient  
const state={
db:null
}
module.exports.connect=function(done){
const url='mongodb://localhost:27017'
const dbname='shopping'

mongoClient.connect(url,(err,data)=>{
    if(err) return done(err)
    state.db=data.db(dbname)

    done()
})

}

module.exports.get=function(){
return state.db
}