Node.js deploys will run "build" script automatically beginning March 11

Change effective on 11 February 2019

Beginning March 11. 2019, Node.js deployments will automatically execute an app’s build script during build if one is defined in the app’s package.json file:

"scripts": {
  "start": "node src/index.js",
  "build": "webpack" // This command will automatically run on deployment

If a heroku-postbuild script is also defined, it will be run instead of the build script.

You can opt in to this change any time before March 11 by setting the heroku-run-build-script key in your package.json file. Opting in now helps prevent any potential disruption to your workflow when this change rolls out.

"scripts": {
    "start": "node src/index.js",
    "build": "webpack"
"heroku-run-build-script": true

To assist with this change, Heroku provides an npm package that updates your package.json file for you. You can run it with one command in your app’s root directory:

$ npx @heroku/update-node-build-script

For more information, please see the FAQ.