Dynamic Feature Toggling in Angular

Implementing feature toggles allows for granular control over the visibility and functionality of features within an application. This is crucial for A/B testing, gradual rollouts, and quickly disabling problematic features without redeploying the entire application. This challenge requires you to build a robust feature toggling system in an Angular application.

Problem Description

You need to create a service and associated mechanisms in an Angular application to manage and dynamically control the availability of different features. The system should allow features to be enabled or disabled based on configuration data, which can be fetched from an external source or defined within the application.

Key Requirements:

1. Feature Toggle Service: Create an Angular service (FeatureToggleService) that will be responsible for managing feature flags.
2. Configuration: The service should be able to load feature flag configurations. Initially, you can hardcode a configuration object, but the design should accommodate fetching this from an API or environment variables.
3. Toggle Status: The service must provide a way to check if a specific feature is currently enabled or disabled.
4. Conditional Rendering: Implement a directive (FeatureToggleDirective) that can be used in component templates to conditionally render HTML elements or components based on feature flag status.
5. Conditional Logic: Demonstrate how to use the FeatureToggleService within a component's TypeScript logic to conditionally execute code.
6. Dynamic Updates (Optional but Recommended): Consider how the system could support updating feature flags dynamically without requiring a full application refresh.

Expected Behavior:

• When a feature is enabled in the configuration, elements using the FeatureToggleDirective with that feature's key should be visible.
• When a feature is disabled, those elements should not be rendered.
• Component logic should be able to access the FeatureToggleService to make decisions based on feature flag status.

Edge Cases to Consider:

• What happens if a requested feature toggle key does not exist in the configuration?
• How will initial configuration loading be handled (e.g., synchronous vs. asynchronous)?

Examples

Example 1: Basic Feature Toggle in Template

Assume the following feature toggle configuration:

{
  "newDashboard": true,
  "oldUserProfile": false
}

Template Snippet:

<!-- This section should be visible -->
<div *featureToggle="'newDashboard'">
  <h2>Welcome to the New Dashboard!</h2>
  <p>This is a brand new experience.</p>
</div>

<!-- This section should NOT be visible -->
<div *featureToggle="'oldUserProfile'">
  <h2>Legacy User Profile</h2>
  <p>Accessing the old profile page.</p>
</div>

<!-- This section should NOT be visible if 'nonExistentFeature' is not in config -->
<div *featureToggle="'nonExistentFeature'">
  <p>This feature is not configured.</p>
</div>

Explanation: The newDashboard feature is true, so the first div is rendered. The oldUserProfile is false, so the second div is not rendered. The nonExistentFeature is not in the configuration, so the third div is also not rendered (or its else block, if provided).

Example 2: Conditional Logic in Component

Assume the same configuration as Example 1.

Component TypeScript:

import { Component, OnInit } from '@angular/core';
import { FeatureToggleService } from './feature-toggle.service'; // Assuming service path

@Component({
  selector: 'app-user-profile',
  templateUrl: './user-profile.component.html',
})
export class UserProfileComponent implements OnInit {
  profileMessage: string = '';

  constructor(private featureToggleService: FeatureToggleService) {}

  ngOnInit(): void {
    if (this.featureToggleService.isEnabled('newDashboard')) {
      this.profileMessage = 'Loading new dashboard features...';
      // ... logic to load new dashboard data
    } else if (this.featureToggleService.isEnabled('oldUserProfile')) {
      this.profileMessage = 'Loading legacy user profile...';
      // ... logic to load legacy profile data
    } else {
      this.profileMessage = 'Feature availability is uncertain. Please contact support.';
    }
  }
}

Explanation: The UserProfileComponent checks if newDashboard is enabled. If so, it sets a specific message and would execute further logic related to the new dashboard. If newDashboard is disabled and oldUserProfile is enabled, it would proceed with the legacy logic. If neither is enabled, a fallback message is used.

Constraints

• The application must be an Angular application using TypeScript.
• The FeatureToggleService should be injectable.
• The FeatureToggleDirective should be a structural directive (using *).
• Initial configuration can be hardcoded as a TypeScript object within the service for simplicity.
• The solution should be mindful of performance, especially when checking toggles frequently.

Notes

• Consider how you will provide the initial feature flag configuration to the FeatureToggleService. An APP_INITIALIZER or a service that is injected first could be good candidates.
• For more advanced scenarios, explore libraries like ngx-feature-flags or angular-feature-flags as inspiration, but aim to build your own core logic for this challenge.
• Think about error handling for missing configurations or potential network issues if fetching from an API.
• The FeatureToggleDirective might benefit from an else clause to render alternative content when a feature is disabled.