testExpress.js

const { apolloExpress, graphiqlExpress  } = require('apollo-server');
const { makeExecutableSchema } = require('graphql-tools')
const express = require('express')
const cors = require('cors')
const bodyParser = require('body-parser')

//Your schema declaration herte
const typeDefs = require('./schema')
const schemaOptions = {
    typeDefs,
    resolvers,
    // allowUndefinedInResolve:true,
    // resolverValidationOptions: {
    //     requireResolversForNonScalar: false
    // }
}
const schema = makeExecutableSchema(schemaOptions)

app.use(cors())

app.use('/graphql',
     bodyParser.json(), 
     apolloExpress({ 
        schema
     })
)
app.use('/graphiql', graphiqlExpress({
  endpointURL: '/graphql',
}));
app.listen(process.env.PORT || 4000,  "0.0.0.0", () => console.log(`Now browse to localhost:${process.env.PORT || 4000}/graphiql for UI or localhost:${process.env.PORT || 4000}/graphql for API`));