Why are my Node.js app modules "not found" when booting the app?
Node.js builds or processes are failing with a module "not found" error.
Heroku doesn't install
devDependencies by default as it is considered a production environment https://devcenter.heroku.com/articles/nodejs-support#devdependencies
You can either move any required packages to the
dependencies section of
package.json, or you can choose to install
devDependencies during the build by running:
heroku config:set NPM_CONFIG_PRODUCTION=false