Heroku local files. Why doesn't app.use(express.static(__dirname + '/public')) work?

Question

Node.js

Tried about as many options:
1) app.use(express.static(__dirname + '/public')); (only works on LAN)
2) app.use(express.static(path.join(__dirname, 'public'))); (local only)
3) app.use(express.static(process.env.PWD + '/public')); (does not work on heroku)
4) app.use("/public", express.static(__dirname + '/public')); (locally)
None of the options above worked for me on heroku.
package.json:

{
  "name": "node-js-getting-started",
  "version": "0.0.2",
  "description": "Sasa",
  "engines": {
    "node": "6.11.1"
  },
  "main": "index.js",
  "scripts": {
    "start": "node index.js",
    "test": "node test.js"
  },
  "dependencies": {
    "ejs": "2.5.6",
    "express": "^4.15.4",
    "socket.io": "^2.0.3"
  },
  "devDependencies": {
    "request": "^2.81.0",
    "tape": "^4.7.0"
  },
  "repository": {
    "type": "git",
    "url": "https://github.com/heroku/node-js-getting-started"
  },
  "keywords": [
    "node",
    "heroku",
    "express"
  ],
  "license": "MIT"
}

And yes, I downloaded node-js-getting-started, and the option with __dirname is also used there.
Thank you.