Bootstrap with Gulp app won't launch from Heroku - node.js

Question

I have a web site built with Bootstrap and Gulp on a NodeJS framework. Gulp basically just compiles changes and routes things, but isn't a server. I have my package.json file scripts section set to run Gulp on start. I have pushed everything to Github and then to Heroku for deployment. When I try to launch it from Heroku, nothing happens. I just get the following message: An error occurred in the application and your page could not be served. If you are the application owner, check your logs for details. Below is the log and my package.json file. Do I need to go back and add something like Express/server.js just to get it to run (with dynamic port setting)?
{
"name": "bs4starter",
"version": "1.0.0",
"description": "Bootstrap 4 workflow",
"main": "index.js",
"scripts": {
"start": "gulp"
},
"author": "Justin Bridwell",
"license": "MIT",
"dependencies": {
"bootstrap": "4.0.0-beta",
"font-awesome": "^4.7.0",
"jquery": "^3.2.1",
"popper.js": "^1.12.0"
},
"devDependencies": {
"browser-sync": "^2.18.13",
"gulp": "^3.9.1",
"gulp-sass": "^3.1.0"
}
}
Here is the Heroku log:
2018-02-20T21:46:01.209374+00:00 app[web.1]: npm ERR! Failed at the
bs4starter#1.0.0 start script.
2018-02-20T21:46:01.209612+00:00 app[web.1]: npm ERR! This is probably not
a problem with npm. There is likely additional logging output above.
2018-02-20T21:46:01.223672+00:00 app[web.1]:
2018-02-20T21:46:01.224004+00:00 app[web.1]: npm ERR! A complete log of
this run can be found in:
2018-02-20T21:46:01.224195+00:00 app[web.1]: npm ERR!
/app/.npm/_logs/2018-02-20T21_46_01_217Z-debug.log
2018-02-23T14:23:21.846098+00:00 heroku[router]: at=error code=H10
desc="App crashed" method=GET path="/" host=polar-caverns-
42095.herokuapp.com request_id=5e788478-e16d-4f2e-a060-106ab9ec81ed
fwd="73.147.231.118" dyno= connect= service= status=503 bytes=
protocol=https
2018-02-23T14:23:22.058194+00:00 heroku[router]: at=error code=H10
desc="App crashed" method=GET path="/favicon.ico" host=polar-caverns-
42095.herokuapp.com request_id=0833d754-afce-48fd-94f7-25900fb9d4cd
fwd="73.147.231.118" dyno= connect= service= status=503 bytes=
protocol=https
2018-02-26T21:26:20.770745+00:00 heroku[router]: at=error code=H10
desc="App crashed" method=GET path="/" host=polar-caverns-
42095.herokuapp.com request_id=6fc50be9-40aa-4922-9a76-955947e78478
fwd="73.147.231.118" dyno= connect= service= status=503 bytes=
protocol=https
2018-02-26T21:26:21.390897+00:00 heroku[router]: at=error code=H10
desc="App crashed" method=GET path="/favicon.ico" host=polar-caverns-
42095.herokuapp.com request_id=73f17c20-7aa3-48d0-86df-5bd5f4dea85a
fwd="73.147.231.118" dyno= connect= service= status=503 bytes=
protocol=https
2018-02-27T13:31:51.110344+00:00 heroku[router]: at=error code=H10
desc="App crashed" method=GET path="/" host=polar-caverns-
42095.herokuapp.com request_id=06f192f8-c5a2-4327-bef1-dc3d9dfa27b2
fwd="73.147.231.118" dyno= connect= service= status=503 bytes=
protocol=https
2018-02-27T13:31:51.317319+00:00 heroku[router]: at=error code=H10
desc="App crashed" method=GET path="/favicon.ico" host=polar-caverns-
42095.herokuapp.com request_id=c02a6c07
-98f4-4b3e-b2c6-c3636e6123e9 fwd="73.147.231.118" dyno= connect= service=
status=503 bytes= protocol=https