How to isolate environment variables from imported modules in Node.js applications?

Other Questions NPM
1

I’m working on a Node.js project where I have multiple JavaScript files that serve dual purposes. Each file can run independently as a test suite and also exports objects for use in other files.

I want to pass configuration parameters when executing files like this:
npm run test-suite --config=banner-test

This allows me to either run all tests with npm run test-suite or target specific tests using npm run test-suite --config=specific-test.

My main file looks like this:

// testRunner.js
const dashboardTests = require('./dashboard/dashboardTests.js');
const userTests = require('./users/userTests.js');
const testFiles = {...dashboardTests.testFiles, ...userTests.testFiles};
let testSpecs = Object.values(testFiles);

if (process.env.npm_config_config) {
    const selectedTest = testFiles[process.env.npm_config_config];
    if (selectedTest) {
        testSpecs = selectedTest;
    }
    else {
        console.error(`Configuration "${process.env.npm_config_config}" not found.`);
        process.exit(1);
    }
}
// execute tests

And my sub-modules have similar logic:

// dashboardTests.js
const testFiles = {
   "banner-test":"./bannerTest.spec.js",
   "sidebar-test":"./sidebarTest.spec.js",
};
let testSpecs = Object.values(testFiles);

if (process.env.npm_config_config) {
    const selectedTest = testFiles[process.env.npm_config_config];
    if (selectedTest) {
        testSpecs = selectedTest;
    }
    else {
        console.error(`Configuration "${process.env.npm_config_config}" not found.`);
        process.exit(1);
    }
}
// run tests
module.exports = {testFiles};

The problem is when I run npm run test-suite --config=banner-test, the environment variable gets passed to all required files, including userTests.js. Since “banner-test” doesn’t exist in userTests.js, it hits the error condition and exits.

How can I import just the exported objects from these files without executing their internal logic that depends on environment variables?

2

You could also wrap your env logic in an IIFE that only runs when needed. Skip executing the config code at module load - use lazy evaluation so it only runs when called. if (require.main === module) { /* your env logic here */ } works, but I’d rather keep exports clean and move execution into separate functions that run conditionally.

3

You need to split your modules - separate the executable logic from what you’re exporting. The problem is your modules are running configuration-dependent code at import time, which happens whether you’re running the file directly or importing it. Move all the environment variable processing and test execution logic into a separate function that only runs when the file is executed directly. Use require.main === module to detect this. Here’s how I’d fix your dashboardTests.js:

const testFiles = {
   "banner-test":"./bannerTest.spec.js",
   "sidebar-test":"./sidebarTest.spec.js",
};

function runTests() {
    let testSpecs = Object.values(testFiles);
    
    if (process.env.npm_config_config) {
        const selectedTest = testFiles[process.env.npm_config_config];
        if (selectedTest) {
            testSpecs = selectedTest;
        } else {
            console.error(`Configuration "${process.env.npm_config_config}" not found.`);
            process.exit(1);
        }
    }
    // run tests here
}

if (require.main === module) {
    runTests();
}

module.exports = {testFiles};

Now when you import the module, you only get the testFiles object without any side effects from environment variable processing.

4

You can also restructure your module exports to avoid running any logic during import. Don’t process environment variables at the module level - create a factory function that handles configuration only when you call it explicitly. Here’s how your dashboardTests.js would look:

const testFiles = {
   "banner-test":"./bannerTest.spec.js",
   "sidebar-test":"./sidebarTest.spec.js",
};

function createTestRunner(config) {
    let testSpecs = Object.values(testFiles);
    
    if (config) {
        const selectedTest = testFiles[config];
        if (selectedTest) {
            testSpecs = selectedTest;
        } else {
            throw new Error(`Configuration "${config}" not found.`);
        }
    }
    return testSpecs;
}

module.exports = { testFiles, createTestRunner };

Now your main testRunner.js just calls createTestRunner(process.env.npm_config_config) for modules that need specific configuration. The imported modules stay completely passive until you explicitly invoke their functionality.