A retry interceptor can be used to automatically retry failed HTTP requests, which can be helpful in handling intermittent network issues.

import { Injectable } from '@angular/core';
import {
  HttpInterceptor,
  HttpRequest,
  HttpHandler,
} from '@angular/common/http';
import { retry } from 'rxjs/operators';

@Injectable()
export class RetryInterceptor implements HttpInterceptor {

  intercept(
    request: HttpRequest<unknown>, 
    next: HttpHandler
  ) {
    // Define the maximum number of retries
    const maxRetries = 3;

    return next.handle(request)
               .pipe(retry(maxRetries));
  }
}

An offline mode interceptor can be used to detect when the user’s device is offline and handle HTTP requests accordingly, such as storing them for later or showing a friendly message.

import { Injectable } from '@angular/core';
import {
  HttpInterceptor,
  HttpRequest,
  HttpHandler,
  HttpErrorResponse,
} from '@angular/common/http';
import { throwError } from 'rxjs';
import { catchError } from 'rxjs/operators';

@Injectable()
export class OfflineModeInterceptor implements HttpInterceptor {
  intercept(
    request: HttpRequest<unknown>, 
    next: HttpHandler
  ) {
    if (!navigator.onLine) {
      console.error(
         'Device is offline. Request not sent:', 
         request.url
      );
      return throwError(
         new HttpErrorResponse({ 
           status: 0, 
           statusText: 'Offline' 
         })
      );
    }

    return next.handle(request);
  }
}

A JWT refresh token interceptor can be used to automatically refresh expired JSON Web Tokens (JWTs) and seamlessly continue making authenticated requests.

import { Injectable } from '@angular/core';
import {
  HttpInterceptor,
  HttpRequest,
  HttpHandler,
  HttpErrorResponse,
} from '@angular/common/http';
import { AuthService } from './auth.service';
import { catchError, switchMap } from 'rxjs/operators';
import { throwError } from 'rxjs';

@Injectable()
export class JwtRefreshInterceptor implements HttpInterceptor {
  constructor(private authService: AuthService) {}

  intercept(
    request: HttpRequest<unknown>, 
    next: HttpHandler
  ) {
    return next.handle(request).pipe(
      catchError((error: HttpErrorResponse) => {
        if (
          error.status === 401 
         && error.error 
         && error.error.message === 'Token expired'
       ) {

          return this.authService.refreshToken().pipe(
            switchMap(() => {
              // Retry the original 
              // request with the new token
              const token = `Bearer ${
                this.authService.getAccessToken()
              }`;
              const updatedRequest = request.clone({
                setHeaders: { Authorization: token },
              });
              return next.handle(updatedRequest);
            }),
            catchError(() => {
              // Refresh token failed; 
              // log out the user or 
              // handle the error
              // For example, you can 
              // redirect to the login page
              this.authService.logout();
              const msg = 'Token refresh failed';
              return throwError(msg);
            })
          );
        }
        return throwError(error);
      })
    );
  }
}

A request timing interceptor can be used to measure and log the time taken for each HTTP request, helping you identify performance bottlenecks.

import { Injectable } from '@angular/core';
import {
  HttpInterceptor,
  HttpRequest,
  HttpHandler,
} from '@angular/common/http';
import { tap } from 'rxjs/operators';

@Injectable()
export class RequestTimingInterceptor implements HttpInterceptor {
  intercept(
    request: HttpRequest<unknown>, 
    next: HttpHandler
  ) {
    const msg = `
      Request to ${request.url} took ${duration}ms
    `;
    const startTime = Date.now();
    return next.handle(request)
      .pipe(
        tap(() => {
          const endTime = Date.now();
          const duration = endTime - startTime;
          console.log(msg);
        })
      );
  }
}

A localization interceptor can be used to automatically include the user’s preferred language or locale in HTTP requests, ensuring that the server sends responses in the appropriate language.

import { Injectable } from '@angular/core';
import {
  HttpInterceptor,
  HttpRequest,
  HttpHandler,
} from '@angular/common/http';
import { LocaleService } from './locale.service';

@Injectable()
export class LocalizationInterceptor implements HttpInterceptor {
  constructor(private localeService: LocaleService) {}

  intercept(
    request: HttpRequest<unknown>, 
    next: HttpHandler
  ) {
    const userLocale = this.localeService.getUserLocale();
    const localizedRequest = request.clone({
      setHeaders: {
        'Accept-Language': userLocale,
      },
    });
    return next.handle(localizedRequest);
  }
}

Creating a custom directive in Angular to handle clicking outside a specific element, like a dropdown or modal, can enhance the user experience by allowing you to close these elements when users interact with the rest of the page. In this example, we’ll create a custom directive named appClickOutside to close a dropdown when users click outside of it.

<div 
  appClickOutside 
  (appClickOutside)="closeDropdown()"
>
  <button (click)="toggleDropdown()">
     Toggle Dropdown
  </button>
  <div 
    *ngIf="dropdownOpen" 
    class="dropdown"
  >
    Dropdown content
  </div>
</div>

import { Directive, ElementRef, Output, EventEmitter, HostListener } from '@angular/core';

@Directive({
  selector: '[clickOutside]'
})
export class ClickOutsideDirective {
  @Output() clickOutside = new EventEmitter<void>();

  constructor(private el: ElementRef) {}

  @HostListener('document:click', ['$event'])
  onClick(event: Event): void {
    const element = this.el.nativeElement;
    if (!element.contains(event.target)) {
      this.appClickOutside.emit();
    }
  }
}

A CSP interceptor can be used to automatically add Content Security Policy headers to outgoing HTTP requests to improve security.

import { Injectable } from '@angular/core';
import {
  HttpInterceptor,
  HttpRequest,
  HttpHandler,
} from '@angular/common/http';

@Injectable()
export class CspInterceptor implements HttpInterceptor {

  intercept(
    request: HttpRequest<any>, 
    next: HttpHandler
  ) {
    const cspHeader = "default-src 'self'; script-src 'self' 'unsafe-inline'";
    const cspRequest = request.clone({
      setHeaders: {
        'Content-Security-Policy': cspHeader,
      },
    });
    return next.handle(cspRequest);
  }
}

A compression interceptor can be used to automatically request compressed content (e.g., gzip) from the server, reducing the amount of data transferred over the network.

import { Injectable } from '@angular/core';
import {
  HttpInterceptor,
  HttpRequest,
  HttpHandler,
} from '@angular/common/http';

@Injectable()
export class CompressionInterceptor implements HttpInterceptor {
  intercept(
    request: HttpRequest<unknown>, 
    next: HttpHandler
  ) {
    const compressedRequest = request.clone({
      setHeaders: { 
        'Accept-Encoding': 'gzip, deflate' 
      },
    });
    return next.handle(compressedRequest);
  }
}

Creating a custom directive in Angular for implementing infinite scrolling can significantly improve the user experience, especially when dealing with long lists of data. In this example, we’ll create a custom directive named appInfiniteScroll to load additional content as the user scrolls down a page.

<div
   appInfiniteScroll 
   class="scrollable-content"
   (scrolled)="loadMoreData()"
>
  <!-- Your list of items -->
</div>

import { Directive, ElementRef, HostListener, Input, Output, EventEmitter } from '@angular/core';

@Directive({
  selector: '[appInfiniteScroll]'
})
export class InfiniteScrollDirective {
  @Input() scrollThreshold = 100;
  @Output() scrolled = new EventEmitter<void>();

  constructor(private el: ElementRef) {}

  @HostListener('scroll', ['$event'])
  onScroll(event: Event): void {
    const {
       scrollHeight,
       scrollTop,
       clientHeight
    } = event.target as HTMLElement;
    const atBottom = scrollHeight - scrollTop <= clientHeight + this.scrollThreshold;

    if (atBottom) {
      this.scrolled.emit();
    }
  }
}