git - Why does Heroku fail to detect Node.js buildpack?

Question

I git cloned a Node.js application (the version specified in the package.json being 4.1.2 and that of my local machine being 6.2.2) and tried to git push on Heroku. But it failed to build and gave this error:

Failed to detect set buildpack https://codon-buildpacks.s3.amazonaws.com/buildpacks/heroku/nodejs.tgz

Now I set the buildpack to heroku/nodejs and I get this message:

Buildpack set. Next release on lit-badlands-92088 will use heroku/nodejs.
Run git push heroku master to create a new release using this buildpack.

Now when I run git push heroku master, I am again told:

remote: -----> Failed to detect set buildpack
        https://codon-buildpacks.s3.amazonaws.com/buildpacks/heroku/nodejs.tgz  

remote: More info: 
https://devcenter.heroku.com/articles/buildpacks#detection-failure  

remote:  
remote:  !     Push failed  
remote: Verifying deploy...  
remote:  
remote: !       Push rejected to lit-badlands-92088.

What could be the possible reasons for the Node.js buildpack not being detected even if I set it?

Answer 1

This means that a package.json file isn't checked into the root of your git project, so Heroku is detecting that it isn't a Node.js app. You can see this locally:

git show master:package.json

To fix it, you'll want to be sure there is a package.json in the root of your project (where there is also a .git directory), and add it to git:

git add package.json
git commit -m 'track package.json'

The phrasing ('failed to detect set buildpack') could be improved. It should probably say 'failed to detect Node.js app'. When the buildpack's "detect" script is run (https://github.com/heroku/heroku-buildpack-nodejs/blob/master/bin/detect), it looks for a package.json file to verify that there's a node app available to build.