Read npm config values from within a Node.js script

Question

Within Node.js, I would like to read the value of the registry property that npm uses to determine where to download packages.

const registry = someApi.get('registry');

I want to know so that I can create a preinstall script that ensures developers are downloading packages through the local Artifactory instance rather than directly from npm.org.

const EXPECTED_REGISTRY = 'https://example.com/artifactory'
const registry = someApi.get('registry'); 
if (registry !== EXPECTED_REGISTRY) {
   console.log('Please configure your .npmrc to use Artifactory');
   console.log('See http://example.com/instructions');
   process.exit(1);
}

One way to do it would be to shell out to npm config list --json. There must be an API that will give me the same result. I'm just having trouble finding it.

Answer 1

While there's already an accepted answer, I'll post an alternative answer for posterity.

If you run your script using the npm command and a script added to the scripts property of your package.json file, then your NPM config properties should be accessible to your NodeJS script via the pattern process.env.npm_config_*.

For example, given this package.json file:

{
  "scripts": {
    "start": "node -p \"process.env.npm_config_foo\""
  }
}

When the following commands are run:

npm config set foo bar
npm start

The output is:

> @ start /Users/anonymous/projects/my-package
> node -p "process.env.npm_config_foo"

bar

Note that if your scripts property is not one of NPM's well-known properties (e.g. test, start), you'll need to use npm run <script-name> instead of npm <script-name>.

Reference: https://docs.npmjs.com/misc/config

Answer 2

I'm quite certain you'll have to "shell out", there's no other API that I'm aware of.

You can utilize nodes execSync() or exec() methods to execute the npm config sub-command get, i.e:

$ npm config get registry

---

Node example using execSync():

const execSync = require('child_process').execSync;

const EXPECTED_REGISTRY = 'https://example.com/artifactory';
const registry = execSync('npm config get registry',
    { stdio: ['ignore', 'pipe', 'pipe'] }).toString().replace(/\n$/, '');

if (registry !== EXPECTED_REGISTRY) {
  console.log('Please configure your .npmrc to use Artifactory');
  console.log('See http://example.com/instructions');
  process.exit(1);
}

Notes:

1. The execSync() option stdio is configured to prevent logging the returned registry value to the console.
2. The regex /\n$/ is utilized to remove the new line character.