在Angular 9中，如果navigator不在线，如何只对http get请求使用缓存

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

@Injectable({
  providedIn: 'root'
})
export class CacheService {
  private cache = new Map<string, HttpResponse<any>>();

  get(req: HttpRequest<any>): HttpResponse<any> | null {
    const url = req.urlWithParams;
    return this.cache.get(url) || null;
  }

  put(req: HttpRequest<any>, res: HttpResponse<any>): void {
    const url = req.urlWithParams;
    this.cache.set(url, res);
  }
}

import { Injectable } from '@angular/core';
import { HttpRequest, HttpResponse, HttpHandler, HttpEvent, HttpInterceptor } from '@angular/common/http';
import { Observable, of } from 'rxjs';
import { tap } from 'rxjs/operators';
import { CacheService } from './cache.service';

@Injectable()
export class CacheInterceptor implements HttpInterceptor {

  constructor(private cacheService: CacheService) {}

  intercept(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    // 只对GET请求进行缓存处理
    if (request.method !== 'GET') {
      return next.handle(request);
    }

    // 检查是否有缓存
    const cachedResponse = this.cacheService.get(request);
    if (cachedResponse) {
      return of(cachedResponse);
    }

    // 发送请求并缓存响应
    return next.handle(request).pipe(
      tap(event => {
        if (event instanceof HttpResponse) {
          this.cacheService.put(request, event);
        }
      })
    );
  }
}

import { NgModule } from '@angular/core';
import { HTTP_INTERCEPTORS } from '@angular/common/http';
import { CacheInterceptor } from './cache.interceptor';

@NgModule({
  providers: [
    { provide: HTTP_INTERCEPTORS, useClass: CacheInterceptor, multi: true }
  ]
})
export class InterceptorModule { }