This worked for me.
mongoose.Promise = global.Promise;
.connect(
"mongodb://127.0.0.1:27017/mydb",
{ useNewUrlParser: true, useCreateIndex: true, useUnifiedTopology: true}).then(db => {
console.log("Database connected");
}).catch(error => console.log("Could not connect to mongo db " + error));
I was using localhost, so i changed it to:
mongodb://127.0.0.1:27017/mydb