How to pass a param to HttpInterceptor?

Question

I am using Angular 4.3.1 and HttpClient. There is an HttpInterceptor to set some headers.

In some http get requests I need to set a different header. Is there anywa

Answer 1

I wrote an interceptor for handling Http error responses. I wanted to allow specific Http calls to instruct the interceptor to ignore certain response status codes, while also retaining the ability to pass params to the Http call. Here is the solution I ended up with. (Thanks, Aleksey for the initial idea in your answer).

Extend HttpParams:

import { HttpParams } from '@angular/common/http';
import { HttpParamsOptions } from '@angular/common/http/src/params';

// Cause the HttpErrorInterceptor to ignore certain error response status codes like this:
//
//  this.http.get(`URL_HERE`, {
//    params: new InterceptorHttpParams({ statusCodesToIgnore: [400, 401] }, {
//      complete: 'false',
//      offset: '0',
//      limit: '50'
//    })
//  })

export class InterceptorHttpParams extends HttpParams {
  constructor(
    public interceptorConfig: { statusCodesToIgnore: number[] },
    params?: { [param: string]: string | string[] }
  ) {
    super({ fromObject: params } as HttpParamsOptions);
  }
}

Interceptor:

intercept(req: HttpRequest, next: HttpHandler): Observable> {
  return next.handle(req).pipe(
    tap(
      () => {},
      (error: any) => {
        if (error instanceof HttpErrorResponse) {
          const regEx = /^[4-5][0-9][0-9]$/; // 4XX and 5XX status codes

          if (regEx.test(error.status.toString())) {
              const errorMessage = this.getErrorMessageFromStatus(error.status);

              if (!this._shouldIgnoreError(req, error)) {
                console.log(`ERROR INTERCEPTOR: ${error.status}`);
                this.toastService.alert(errorMessage);
              }
          }
        }
      })
  );
}

// Based on `request.params.interceptorConfig.statusCodesToIgnore`, we can see if we should ignore this error.
_shouldIgnoreError(request: HttpRequest, errorResponse: HttpErrorResponse) {
  if (request.params instanceof InterceptorHttpParams
    && Array.isArray(request.params.interceptorConfig.statusCodesToIgnore)
    && request.params.interceptorConfig.statusCodesToIgnore.includes(errorResponse.status)) {

    return true;
  }

  return false;
}