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It seems that your node-gyp requires java to be built correctly. The thing with Heroku's architecture is that it only provides you what you specify/need. Right now I don't think Heroku understands that it needs a JVM to run your application. So you should provide a buildpack. A build pack put very simply is a set of rules telling Heroku what to set-up, install and build. There is a buildpack for JVM called heroku/jvm. So, what you have to do is add this to your application through the dashboard or your CLI via heroku buildpacks:add heroku/jvm.

There is one more thing to do. Since your app requires javac at build time itself, we should pull up the build order for java/jvm . So in that case you should probably do heroku buildpacks:add --index 1 heroku/jvm. This puts the JVM buildpack at position 1 and pushes every other buildpack down the order.

Now when the app starts building, it first sets up the JVM (thus enabling javac for your instance) and then runs the NodeJS build. This build will now pick up the javac from the current instance and build accordingly.

Ref: Mulitple Buildpacks in Heroku

As of JavaFX 8.0, you can call