Why are all my Mongoose requests timing out?

First you need to wait a connection to be established to make sure it will be ok, see Error handling:

try {  await mongoose.connect('mongodb://localhost:27017/test', { useNewUrlParser: true });} catch (error) {  handleError(error);}

Second you need to call mongoose.connection.close() after save call will be either resolved or rejected:

exampleOne.save().then(res => {  console.log(res)  mongoose.connection.close()})

because you didn't use await the save call didn't wait for resolve and mongoose.connection.close() was immediately called.

const res = await exampleOne.save()console.log(res)mongoose.connection.close()})

As I said in comment and also @Anatoly said you should send request (i.e. save) after that connection was established.

const mongoose = require('mongoose')const exampleSchema = new mongoose.Schema({  title: String,  author: String})const Example = mongoose.model('Example', exampleSchema)const mongoURL = //replace this comment with your own Mongo URLmongoose.connect(mongoURL, {   useNewUrlParser: true,   useUnifiedTopology: true,   useFindAndModify: false,   useCreateIndex: true }).then(() => {  const exampleOne = new Example({    title: 'Don Quixote',    author: 'M. Cervantes'  })  exampleOne.save().then(res => {    console.log(res)    mongoose.connection.close()  })}).catch(err => {  // handle error})