problem

The following code does work.

const MONGODB_URL = `mongodb://${process.env.DB_USERNAME}:${process.env.DB_PASSWORD}@localhost:27017`;

mongoose.connect(MONGODB_URL);

  async () => {
    console.log("Cron Job Working");
    try {
      const result = await dummyData.save();
      console.log("create succeeded");
    } catch (e) {
      console.log(e);
    }

But the following code doesn't work.

const MONGODB_URL = `mongodb://${process.env.DB_USERNAME}:${process.env.DB_PASSWORD}@localhost:27017/db`;

mongoose.connect(MONGODB_URL);

  async () => {
    console.log("Cron Job Working");
    try {
      const result = await dummyData.save();
      console.log("create succeeded");
    } catch (e) {
      console.log(e);
    }

cause of problem

URL is needed additional parameter of authSource when you point out db name explicitly.

Correct URL

const MONGODB_URL = `mongodb://${process.env.DB_USERNAME}:${process.env.DB_PASSWORD}@localhost:27017/world_info?authSource=admin`;

Happy coding!

reference👇
https://stackoverflow.com/questions/62818786/mongoose-connection-error-when-using-db-name-in-connection-string