I have server.js and db.js The db.js file interacts with my database using Mongoose and I use server.js to call functions
I encountered this error when running the populatedb.js script in the MDN tutorial for Express/NodeJS.
The script was looking for a db connection starting with mongodb://, however my connection string from mongo started with mongodb+srv://.
I edited the script to check for this syntax instead, which resolved the error.
I hope this helps someone.