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Grokking Node.js Design Patterns for Interviews

Problem: Adapt Configuration Sources

Medium
30 min
Unify environment, file-based, and remote configuration providers under a single .get(key) interface.

Problem statement

Your system reads configuration values from different sources depending on the deployment environment:

  • Environment variables via process.env.

  • JSON config file for local development.

  • Remote config service in production, which fetches values asynchronously.

Each source has a different interface:

  • The env provider reads synchronously via property access.

  • The file provider loads from an object in memory.

  • The remote provider exposes an async .fetch(key) method.

To simplify configuration access across your codebase, you need an adapter that makes all three sources behave uniformly.

Goal

Implement a ConfigAdapter class exposing an async method:

async get(key)

It should:

  • Return the correct value from the underlying provider.

  • Normalize sync and async differences.

  • Always resolve to null if the key doesn’t exist.

Constraints

  • You cannot modify the original providers.

  • The adapter must support all three data sources.

  • All calls to .get() should be awaitable.

  • Avoid environment conditionals (if (env === 'prod')); use capability detection instead.

Sample output

The examples below illustrate what the output should look like:

(async () => {
  const envConfig = new ConfigAdapter(envProvider);
  const fileConfig = new ConfigAdapter(fileProvider);
  const remoteConfig = new ConfigAdapter(remoteProvider);
  console.log(await envConfig.get('PATH'));
  console.log(await fileConfig.get('apiUrl'));
  console.log(await remoteConfig.get('apiUrl'));
})();
/* Expected output:
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
http://localhost:3000
https://api.prod.com
*/

Good luck trying the problem! If you’re unsure how to proceed, check the “Solution” tab above.

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Standardize File Storage Clients
Bridge Callback and Promise APIs
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Asynchronous Streaming Adapter
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Home
Courses
Grokking Node.js Design Patterns for Interviews

Problem: Adapt Configuration Sources

Medium
30 min
Unify environment, file-based, and remote configuration providers under a single .get(key) interface.

Problem statement

Your system reads configuration values from different sources depending on the deployment environment:

  • Environment variables via process.env.

  • JSON config file for local development.

  • Remote config service in production, which fetches values asynchronously.

Each source has a different interface:

  • The env provider reads synchronously via property access.

  • The file provider loads from an object in memory.

  • The remote provider exposes an async .fetch(key) method.

To simplify configuration access across your codebase, you need an adapter that makes all three sources behave uniformly.

Goal

Implement a ConfigAdapter class exposing an async method:

async get(key)

It should:

  • Return the correct value from the underlying provider.

  • Normalize sync and async differences.

  • Always resolve to null if the key doesn’t exist.

Constraints

  • You cannot modify the original providers.

  • The adapter must support all three data sources.

  • All calls to .get() should be awaitable.

  • Avoid environment conditionals (if (env === 'prod')); use capability detection instead.

Sample output

The examples below illustrate what the output should look like:

(async () => {
  const envConfig = new ConfigAdapter(envProvider);
  const fileConfig = new ConfigAdapter(fileProvider);
  const remoteConfig = new ConfigAdapter(remoteProvider);
  console.log(await envConfig.get('PATH'));
  console.log(await fileConfig.get('apiUrl'));
  console.log(await remoteConfig.get('apiUrl'));
})();
/* Expected output:
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
http://localhost:3000
https://api.prod.com
*/

Good luck trying the problem! If you’re unsure how to proceed, check the “Solution” tab above.

Similar Problems
Normalize Logger Interfaces
Standardize File Storage Clients
Bridge Callback and Promise APIs
Unify Cache Clients
Compose Nested Adapters
Hybrid Service Adapter for Fallback APIs
Asynchronous Streaming Adapter
Unify HTTP Client Responses
Node.js
// Simulated environment variable provider
const envProvider = {
  getValue(key) {
    return process.env[key] ?? null;
  }
};
// Simulated JSON config provider
const fileProvider = {
  config: { apiUrl: 'http://localhost:3000', debug: true },
  read(key) {
    return this.config[key] ?? null;
  }
};
// Simulated remote config provider
const remoteProvider = {
  async fetch(key) {
    return new Promise(resolve => {
      setTimeout(() => {
        const remoteConfig = { apiUrl: 'https://api.prod.com', debug: false };
        resolve(remoteConfig[key] ?? null);
      }, 100);
    });
  }
};
// Your code here
// Example usage
(async () => {
  const envConfig = new ConfigAdapter(envProvider);
  const fileConfig = new ConfigAdapter(fileProvider);
  const remoteConfig = new ConfigAdapter(remoteProvider);
  console.log(await envConfig.get('PATH'));
  console.log(await fileConfig.get('apiUrl'));
  console.log(await remoteConfig.get('apiUrl'));
})();
/* Expected output:
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
http://localhost:3000
https://api.prod.com
*/