http-error.interceptor.ts

import {
  HttpEvent,
  HttpInterceptor,
  HttpHandler,
  HttpRequest,
  HttpResponse,
  HttpErrorResponse
} from '@angular/common/http';
import {Observable, throwError} from 'rxjs';
import {retry, catchError} from 'rxjs/operators';
import {Component, Input} from '@angular/core';


export class HttpErrorInterceptor implements HttpInterceptor {
  intercept(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    return next.handle(request)
      .pipe(
        retry(1),
        catchError((error: HttpErrorResponse) => {
          let errorMessage = '';
          if (error.error instanceof ErrorEvent) {
            // client-side error
            errorMessage = `Error: ${error.error.message}`;
          } else if (error.message === 'Http failure response for http://sd5-backend.engr.uconn.edu/auth: 404 Not Found') {
            window.alert('Invalid Credentials');

          } else {
            // server-side error
            errorMessage = `Error Code: ${error.status}\nMessage: ${error.message}`;
          }

          return throwError(errorMessage);
        })
      );
  }
}