NodeJS Mongoose can connect from one linux directory but not another - node.js

Question

Several months ago, I set up a production NodeJS app that uses mongoose to connect to a MongoDB database with the following connection string:
mongodb://#127.0.0.1:27017/invoice_app?retryWrites=true&w=majority
I did not need to supply a username or password and everything worked.
I wanted to make a copy of the NodeJS project on the same server and point it to the same database. I'll call this the staging NodeJS project. However, everytime I try to npm start my staging project, I get the error (node:11495) UnhandledPromiseRejectionWarning: MongoParseError: No username provided in authority section.
As far as I can tell, this staging project is the exact same as the production one. Line by line, they should be the same, except they are in different directories. I reused the exact same connection string. The NodeJS project is used owned/executed by the same user.
Why can mongoose connect from one directory but not another? Is there something else I completely misunderstood?

Answer 1

The issue was that I had deleted the node_modules directory from my staging project along the way. And when I ran the npm install in the staging directory, it didn't actually give me the correct node_modules package versions as production. Here was the relevant lines from package-lock.json that resolved my issues in staging:
"mongodb": {
"version": "3.3.5",
"resolved": "https://registry.npmjs.org/mongodb/-/mongodb-3.3.5.tgz",
"integrity": "sha1-ONUxATr+3pKw3SguO588CMm9/zs=",
"requires": {
"bson": "^1.1.1",
"require_optional": "^1.0.1",
"safe-buffer": "^5.1.2",
"saslprep": "^1.0.0"
}
},
"mongoose": {
"version": "5.7.13",
"resolved": "https://registry.npmjs.org/mongoose/-/mongoose-5.7.13.tgz",
"integrity": "sha1-2Ou8Fc+xnQFM8fvUt69BPXWVLUY=",
"requires": {
"bson": "~1.1.1",
"kareem": "2.3.1",
"mongodb": "3.3.5",
"mongoose-legacy-pluralize": "1.0.2",
"mpath": "0.6.0",
"mquery": "3.2.2",
"ms": "2.1.2",
"regexp-clone": "1.0.0",
"safe-buffer": "5.1.2",
"sift": "7.0.1",
"sliced": "1.0.1"
},
"dependencies": {
"ms": {
"version": "2.1.2",
"resolved": "https://registry.npmjs.org/ms/-/ms-2.1.2.tgz",
"integrity": "sha1-0J0fNXtEP0kzgqjrPM0YOHKuYAk="
}
}
},
"mongoose-legacy-pluralize": {
"version": "1.0.2",
"resolved": "https://registry.npmjs.org/mongoose-legacy-pluralize/-/mongoose-legacy-pluralize-1.0.2.tgz",
"integrity": "sha1-O6n5H6UHtRhtOZ+0CFS/8Y+1Y+Q="
},