vaadin-maven-plugin npm registry configuration - node.js

Question

For context, I'm running a jenkins build which has no direct internet access. We have a nexus with proxy repositories for maven, nodejs and npm.
I'm using the recommended frontend-maven-plugin to download and install node and npm. This step works fine. Afterwards the vaadin-maven-plugin is used with the prepare-frontend and build-frontend goals.
Apparently, this triggers the actual npm install so I need it to contact the private npm registry, yet I can't find any setting to specify this. I did find a npmRegistryURL variable in the vaadin-maven-plugin configuration, but apparently this isn't used for the build-frontend goal.
My pom setup looks like this:
<build>
<plugins>
<plugin>
<groupId>com.github.eirslett</groupId>
<artifactId>frontend-maven-plugin</artifactId>
<executions>
<execution>
<id>install node and npm</id>
<goals>
<goal>install-node-and-npm</goal>
</goals>
<phase>generate-resources</phase>
</execution>
</executions>
<configuration>
<nodeVersion>v12.13.0</nodeVersion>
<nodeDownloadRoot>https://nexusrepo.com/repository/nodejs/</nodeDownloadRoot>
<npmDownloadRoot>https://nexusrepo.com/repository/npmjs/</npmDownloadRoot>
</configuration>
</plugin>
<plugin>
<groupId>com.vaadin</groupId>
<artifactId>vaadin-maven-plugin</artifactId>
<executions>
<execution>
<id>prep</id>
<goals>
<goal>prepare-frontend</goal>
<goal>build-frontend</goal>
</goals>
</execution>
</executions>
<configuration>
<npmRegistryURL>https://nexusrepo.com/repository/npmjs/</npmRegistryURL>
</configuration>
</plugin>
</plugins>
</build>
I've also tried to let the frontend-maven-plugin handle the npm install but that doesn't work because the vaadin-maven-plugin is manually adding extras to the node_modules/#vaadin folder.
So I got the same Error: Cannot find module '#vaadin/stats-plugin' as specified in Vaadin issue 10306
I've also tried to add a .npmrc file to the root of my project to specify the npm registry, but that had no effect. Should this work or is it simply not checked by the vaadin-maven-plugin?
Some help would be greatly appreciated. I can't manually configure the node installation by using npm config set registry because it's not a static node installation, so the configuration needs to happen inside of the actual maven build.

Answer 1

After quite a bit of searching and testing, there seem to be 2 ways of solving this problem.
Option 1 is to configure the frontend-maven-plugin with an npm execution/goal.
The default argument is install, but it doesn't have to be. That way you can use this execution to run the npm config set registry command.
<execution>
<id>npm config</id>
<goals>
<goal>npm</goal>
</goals>
<configuration>
<arguments>config set registry https://nexusrepo.com/repository/npmjs/</arguments>
</configuration>
<phase>generate-resources</phase>
</execution>
WARNING: from my experience, this saves the given registry in a user folder .npmrc file, which would probably affect every npm build on your jenkins, since it would save it for the default jenkins-user. Therefore, this did not seem like a proper solution.
Option 2 is adding a .npmrc file to the root of your project.
I tried doing this at first but it didn't work (as specified in the question). This only seemed to be the case on my local workstation, probably because I also had nodejs and npm actually installed and the settings were being overridden somewhere else. During the jenkins build this worked as intended.
Option 2 definitely seemed like the better way to go forward, so that's what I did for now. Still annoyed by the lack of vaadin-maven-plugin documentation, but at least I got it to work.