This buildpack is different from the others buildpack which create subdirs because the goal is to have in your project a directory heroku in which you setup a nodejs server. In the postinstall command you go in the correct folder in build your project.
Add as a first buildpack in the chain. Set PROJECT_PATH environment variable to point to project root. It will be promoted to slug's root, everything else will be erased. Following buildpack (e.g. nodejs) will finish slug compilation.
- heroku buildpacks:clear if necessary
- heroku buildpacks:set https://github.com/talkspirit/subdir-heroku-buildpack
- heroku buildpacks:add heroku/nodejs or whatever buildpack you need for your application
- heroku config:set PROJECT_PATH=projects/nodejs/frontend pointing to what you want to be a project root.
- Deploy your project to Heroku.
The buildpack takes subdirectory you configured, erases everything else, and copies that subdirectory to project root. Then normal Heroku slug compilation proceeds.