Detecting your application

Next, you will want to actually detect that the app you are building is a node-js app. In order to do this, you will need to check for a package.json.

Replace exit 1 in the detect script with the following check:

if [[ ! -f package.json ]]; then
   exit 100

Your node-js-buildpack/bin/detect script should look like this:

#!/usr/bin/env bash
set -eo pipefail

if [[ ! -f package.json ]]; then
   exit 100

Next, rebuild your app with the updated buildpack:

pack build test-node-js-app --path ./node-js-sample-app --buildpack ./node-js-buildpack

You should see the following output:

Previous image with name "test-node-js-app" not found
examples/node-js 0.0.1
---> node-js Buildpack
ERROR: failed to build: exit status 1
ERROR: failed to build: executing lifecycle: failed with status code: 51

Notice that detect now passes because there is a valid package.json in the NodeJS app at node-js-sample-app, but now build fails because it is currently written to error out.

You will also notice that RESTORING now appears in the build output. This step is part of the buildpack lifecycle that looks to see if any previous image builds have layers that the buildpack can re-use. We will get into this topic in more detail later.

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