Angular Global Error Handling Strategy

You've encountered a common challenge in Angular development: handling errors consistently across your application. Without a centralized error management system, errors can slip through, leading to a poor user experience and difficult debugging. This challenge will guide you in creating a robust global error handler for your Angular application.

Problem Description

Your task is to implement a global error handler in your Angular application. This handler should intercept all uncaught exceptions that occur in the application, both from asynchronous operations (like HTTP requests) and synchronous code. The goal is to provide a consistent way to log these errors and potentially display a user-friendly message without crashing the entire application.

Key Requirements:

• Intercept Uncaught Errors: The solution must catch all unhandled exceptions thrown within the Angular application lifecycle. This includes errors originating from components, services, pipes, and asynchronous operations.
• Centralized Logging: Implement a mechanism to log all caught errors. This could involve writing to the browser's console, sending them to a remote logging service, or both.
• User-Friendly Feedback: For certain types of errors (e.g., network errors from HTTP requests), the application should ideally display a user-friendly message to the end-user, informing them of the issue without exposing technical details.
• Application Resilience: The application should not completely crash when an error occurs. It should gracefully handle the error and continue running if possible.
• Service Integration: The error handling logic should be encapsulated within an Angular service.

Expected Behavior:

When an uncaught error occurs in the application:

1. The error should be intercepted by your global error handler.
2. The error details (e.g., message, stack trace) should be logged.
3. If the error is identifiable as a user-facing issue (e.g., a 404 Not Found from an API), a toast notification or a similar mechanism should inform the user.
4. The application should remain interactive, and other parts of the application should continue to function.

Edge Cases to Consider:

• Errors occurring during the application's initialization phase.
• Errors within asynchronous operations like setTimeout, setInterval, or Promise.then.
• Errors triggered by third-party libraries.
• HTTP errors that require specific user feedback.

Examples

Example 1: Component Error

Suppose you have a component that tries to access a property of an undefined object:

Component Code (Conceptual):

import { Component } from '@angular/core';

@Component({
  selector: 'app-error-component',
  template: `<div>{{ user.name }}</div>`
})
export class ErrorComponent {
  user: any; // user is undefined
}

Input: User navigates to ErrorComponent.

Output:

• The global error handler intercepts the TypeError: Cannot read properties of undefined (reading 'name').
• The error is logged to the console (e.g., [ERROR] TypeError: Cannot read properties of undefined (reading 'name') at ErrorComponent.ngOnInit...).
• A generic error message might be displayed to the user (e.g., "An unexpected error occurred.").
• The rest of the application remains functional.

Example 2: HTTP Error

Consider an Angular service making an HTTP request that fails with a 404 Not Found status.

Service Code (Conceptual):

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable, throwError } from 'rxjs';
import { catchError } from 'rxjs/operators';

@Injectable({
  providedIn: 'root'
})
export class DataService {
  constructor(private http: HttpClient) {}

  getData(): Observable<any> {
    return this.http.get('/api/non-existent-endpoint').pipe(
      catchError(error => {
        // This error would also be caught by the global handler
        return throwError(() => new Error('Data fetch failed'));
      })
    );
  }
}

Input: A component calls DataService.getData(). The API returns a 404 status.

Output:

• The global error handler intercepts the HttpClient error.
• The error details are logged.
• A user-friendly message is displayed to the user (e.g., "Sorry, the requested data could not be found.").
• The application continues to operate.

Constraints

• The solution must be implemented using TypeScript.
• The error handler should be provided as an Angular ErrorHandler provider.
• The solution should be mindful of performance and not introduce significant overhead.
• Error logging should be directed to console.error by default, but the implementation should be extensible to other logging mechanisms.

Notes

• Angular's ErrorHandler interface is your primary tool for this challenge. You'll need to create a class that implements this interface and provide it in your application's root module.
• Consider how you will differentiate between errors that require user notification and those that are purely for developer debugging.
• Think about potential error sources: component rendering, service calls, asynchronous operations, etc.
• For HTTP errors, you can often inspect the error object for properties like status and statusText to determine the type of error.
• You might want to create a separate service for handling the logging and user notification aspects, which your global error handler can then delegate to.