Questions
Q:

MongooseError: The ‘uri’ parameter to ‘openUri()’ must be a string, got “undefined”

Try to connect MongoDB using mongoose, But get this MongooseError,

MongooseError: The `uri` parameter to `openUri()` must be a string,
got "undefined". Make sure the first parameter to `mongoose.connect()` or `mongoose.createConnection()` is a string.