Why do I obtain this error when deploying app to Heroku?

My silly mistake was that I was pushing the master branch to Heroku while my changes were in another branch!

Make sure that you merge your latest branch with your master branch first

> git checkout master

> git merge your-latest-branch

> git push heroku master

You have to inform heroku where to start : missing script: start. In your package.json, you should have something like this:

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

Where index.js is your entry point.

As an alternative, you can specify in Procfile:

web: node index.js