Heroku: npm Failure - index.js not found

I am trying to set up my "web app" on Heroku. When I double click on my index.html it shows up in my browser but the app fails to open in Heroku. I am accessing my files through github, which is working fine.

In oder to set up my working environment I followed this tutorial exactly: https://www.kirupa.com/react/setting_up_react_environment.htm

After reading about my initial errors in Heroku:

1.) I added the Node Version (But not the npm Version since I only saw how to add one or the other and not both.)

"engines": {
    "node": "7.10.0"},

2.) I changed the Script to:

"scripts": {
      "start": "node index.js"},

That was straight forward enough, but now after running npm start, I see a distinct error (also reflected in the https://www.npmjs.com browser test):

Error: Cannot find module '/Users/MyUser/MyFolder/index.js'

Now, due to that tutorial above, I only have "index.jsx" located within an additional folder like: MyFolder/dev/index.jsx

I tried to change the file extension in package.json and or the file path, but no matter what I do, the file is not being found. I am guessing that ".jsx" should automatically be recognised as ".js", but I think that only because of the way that the tutorial was written...

Please help me figure out how to run npm start without error. Thank you in advance!

via April