Example: Util Service

import { Injectable } from '@angular/core';
import { CurrencyPipe, DatePipe, DecimalPipe, PercentPipe } from '@angular/common';
import { isNumber } from 'util';
import { of, throwError } from 'rxjs';
import { Observable } from 'rxjs/index';
import _ from 'lodash';


@Injectable({
  providedIn: 'root'
})
export class UtilService {
  cp: CurrencyPipe = new CurrencyPipe('en-US');
  dp: DecimalPipe = new DecimalPipe('en-US');
  dtp: DatePipe = new DatePipe('en-US');
  pp: PercentPipe = new PercentPipe('en-US');

  constructor() { }

  /**
   * Generates contents of a flat file based on incoming source data.
   */
  buildFlatFileContent(source: any[]): Observable<string> {
    let fileContents = '';

    try {
      if (Array.isArray(source) && source.length) {
        // Each item of source will be a string representing the entire contents of the row
        fileContents = _.join(source, '\r\n');
      }
    } catch(e) {
      console.error(e);
      return throwError(new Error('There was a problem building the flat file contents.'));
    }

    return of(fileContents);
  }

  /**
   * Called to download a text-based file client-side.
   */
  downloadFile(filename: string, contents: string): Observable<any> {
    let observable = new Observable(subscriber => {
      let blob = new Blob([contents]);


      if (window.navigator && window.navigator.msSaveOrOpenBlob) {
        //Open file IE
        window.navigator.msSaveOrOpenBlob(blob, filename);
        subscriber.complete();
      } else {
        //Open file browser other than IE
        let a = document.createElement('a');
        a.style.display = 'none';
        document.body.appendChild(a);
        a.href = window.URL.createObjectURL(blob);
        a.download = filename;
  
        setTimeout(() => {
          a.click();
          document.body.removeChild(a);
          subscriber.next("Success");
          subscriber.complete();
        }, 500);
      }
    });

    return observable;
  }

  /**
   * Strips currency characters from a currency formatted number
   * string and returns the numeric equivalent.
   */
  currencyToNumber(source: string): number {
    if (!(typeof source === 'string' && source.length)) {
      return NaN;
    }

    let modifiedSource = source.replace(/[$,]/g, '');
    modifiedSource = modifiedSource.replace(/\(/, '-');
    modifiedSource = modifiedSource.replace(/\)/, '');

    return isNaN(Number(modifiedSource)) ? NaN : parseFloat(modifiedSource);
  }

  /**
   * Formats the incoming bytes as a readable string.
   */
  formatFileSize(bytes, decimalPoint) {
    if (bytes == 0) return '0 Bytes';
    let k = 1000;
    let dm = decimalPoint || 2;
    let sizes = ['Bytes', 'KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'];
    let i = Math.floor(Math.log(bytes) / Math.log(k));
    return parseFloat((bytes / Math.pow(k, i)).toFixed(dm)) + ' ' + sizes[i];
  }
}