Currency.ts

/**
 * interfaces fill the role of naming types,
 * and are a powerful way of defining contracts within your code as well as contracts with code outside of your project.
 */
export interface ICurrency {
  readonly label: string;
  readonly value: string;
  readonly currency_name: string;
}
/**
 * create type for Array
 */
export type CurrencyPairs = Array<ICurrency>;

/**
 * create new instance of property that allow to modify elements
 */
export class Currency implements ICurrency {
  public readonly label: string;
  public readonly value: string;
  public readonly currency_name: string;

  constructor(data: ICurrency) {
    this.currency_name = data.currency_name;
    this.value = data.currency_name;
    /**
     * modify currency_name, to add '/' between currency name
     */
    this.label = data.currency_name.replace(new RegExp(`^(.{${3}})(.)`), `$1${'/'}$2`);
  }
}