Error R10 (Boot timeout) -> Web process failed to bind to $PORT within 60 seconds of launch on Heroku with a node.js project

I seem to be getting an R10 timeout error and I can't work out what the issue is? I'm told Heroku uses a default port so i don't know if it's that that is erroring, but where would I set a port?

My procfile is:

web: npm start

and the line in the package.json is:

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