Problem: Create a Feature-Flagged Analytics Service

Hard

40 min

Return either a real analytics service or a stub based on a feature flag, using only factory logic.

Problem statement

You’re rolling out a new analytics module, but it’s not yet available to all users. It’s gated behind a flags.analyticsEnabled feature flag. The team needs a factory that returns either:

A real AnalyticsService when the flag is on.
A stub that does nothing when the flag is off.

Both methods must be exposed: .track() and .report(). This ensures the rest of the codebase can safely call the service without knowing which version was returned.

Goal

Implement createAnalyticsService(flags) that returns either a real or stub service, with matching method signatures.

Constraints

Do not use conditionals (if, switch, ternaries) to select which class to instantiate.
The factory must return an object with .track() and .report() either way.
Stub and real classes must only be instantiated within the factory.

Sample output

The examples below illustrate what the output should look like:

Problem: Create a Feature-Flagged Analytics Service

Hard

40 min

Return either a real analytics service or a stub based on a feature flag, using only factory logic.

Problem statement

You’re rolling out a new analytics module, but it’s not yet available to all users. It’s gated behind a flags.analyticsEnabled feature flag. The team needs a factory that returns either:

A real AnalyticsService when the flag is on.
A stub that does nothing when the flag is off.

Both methods must be exposed: .track() and .report(). This ensures the rest of the codebase can safely call the service without knowing which version was returned.

Goal

Implement createAnalyticsService(flags) that returns either a real or stub service, with matching method signatures.

Constraints

Do not use conditionals (if, switch, ternaries) to select which class to instantiate.
The factory must return an object with .track() and .report() either way.
Stub and real classes must only be instantiated within the factory.

Sample output

The examples below illustrate what the output should look like:

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Node.js

class AnalyticsService {
  constructor() {
    console.log('AnalyticsService initialized');
  }
  track(event) {
    console.log('Tracking event:', event);
  }
  report() {
    console.log('Generating report');
  }
}
// Implement this
function createAnalyticsService(flags) {
  // Return real or stub service based on flags.analyticsEnabled
}
// Example usage
const flags1 = { analyticsEnabled: true };
const analytics1 = createAnalyticsService(flags1);
analytics1.track('user.signup');
analytics1.report();
/* Expected output:
AnalyticsService initialized
Tracking event: user.signup
Generating report */
console.log('---');
const flags2 = { analyticsEnabled: false };
const analytics2 = createAnalyticsService(flags2);
analytics2.track('user.login');
analytics2.report();
/* No output expected */