This function can be used to get files from angular observable

apiHandler.ts

import { HttpClient, HttpHeaders, HttpParams } from "@angular/common/http";
import { Injectable } from "@angular/core";
import { TokenManager } from "@app/shared/services/token-manager.service";

@Injectable()
export class ApiHandler {
  constructor(private http: HttpClient) {}

  apiGet(url, params?, extras?: Extras) {
    let options = this.renderHeaders(extras);
    options = this.appendParams(options, params);
    return this.http.get(url, options).timeout(30000);
  }

  apiPost(url, reqBody, extras?: Extras) {
    const options = this.renderHeaders(extras);
    return this.http.post(url, reqBody, options).timeout(30000);
  }

  apiUpdate(url, reqBody, extras?: Extras) {
    const options = this.renderHeaders(extras);
    return this.http.put(url, reqBody, options).timeout(30000);
  }

  apiDelete(url, extras?) {
    const options = this.renderHeaders(extras);
    return this.http.delete(url);
  }

  private renderHeaders(extras: Extras) {
    // if extras is present then apply check
    if (extras) {
      if (extras.contentType.isFormDataContent) {
        return {};
      }
    } else {
      // else assume it to be json data
      return {
        headers: new HttpHeaders({
          "Content-Type": "application/json"
        })
        // headers: new HttpHeaders({
        //   "Content-Type": "application/xml"
        // })
      };
    }
  }

  getHttpRequester() {
    return this.http;
  }

  private appendParams(originalOptions, paramsObj) {
    let params = new HttpParams();
    for (let key in paramsObj) {
      if (paramsObj.hasOwnProperty(key)) {
        if (key === "offset") {
          const val = paramsObj[key] / 10;
          params = params.append("page_num", val.toString());
        } else {
          params = params.append(key, paramsObj[key]);
        }
      }
    }
    return Object.assign({}, originalOptions, { params: params });
  }
}

fileRequester.ts

  testFun(excelDownloadUrl) {
    this.apiHandler
      .getHttpRequester()
      .get("http://192.168.0.243:3000/api/admin/report/user", {
        responseType: "blob"
      })
      .subscribe(data => {
        console.log(data);
        const blob: any = new Blob([data], {
          type:
            "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet"
        });
        // blob.name = "user-report.xlsx"
        var url = window.URL.createObjectURL(blob);
        const a = document.createElement("a");
        a.href = url;
        a.download = "user-report";
        a.style.display = "none";
        document.body.appendChild(a);
        a.click();
        window.URL.revokeObjectURL(url);
        document.body.removeChild(a);
      });
  }

// call the function on some button click