Node.js uses the implementation session (MongoDB-based) to report an error. What should I do?

  node.js, question

StudyingA simple blogAccording to the content of the article, during the process of building the local environment to realize the function, there was a problem when adding the session part. The error message is as follows. Can a great god help you to look at it? Thank you very much.

报错信息

app.js

In the course of various tests, it was found that
Var dbUrl = “mongodb:// “plus settings.host plus”/”plus settings.db;

app.use(session({
resave: false,
saveUninitialized: true,
secret: settings.cookieSecret,
key: settings.db,
cookie: {

maxAge: 1000 * 60 * 60 * 24 * 30

},
store: new MongoStore({

url: dbUrl

})
}));
In this way, the database can be connected normally and run normally. Can anyone explain?