angular-cn/aio/content/examples/architecture/src/app/sales-tax.service.ts

import { Injectable } from '@angular/core';

import { TaxRateService } from './tax-rate.service';

@Injectable()
export class SalesTaxService {
  constructor(private rateService: TaxRateService) { }

  getVAT(value: string | number) {
    const amount = (typeof value === 'string') ?
      parseFloat(value) : value;
    return (amount || 0) * this.rateService.getRate('VAT');
  }
}