Currency.js override with custom defaults

main.js

import currency from 'currency.js';

// Library docs: https://currency.js.org/
// We create a custom constructor with custom config here

export function customCurrency(value, options) {
  if (value === null || value === undefined) return value; // I don't like that it returns 0.00

  if (!(this instanceof customCurrency)) { // this enables calling the function without 'new'
    return new customCurrency(value, options);
  }

  // Call the 'constructor' of currency.js on this
  currency.call(this, value, {
    errorOnInvalid: true, // otherwise, invalid values will be 0.00
    symbol: '€',
    formatWithSymbol: true,
    ...options,
  });
}

customCurrency.prototype = currency.prototype; // enables check: 'x instanceof customCurrency'

usage.js

const c = customCurrency(1.23) || new customCurrency(1.23); // depending on preference

c.add(1.11) // 2.34

c instanceof customCurrency // true
c instanceof require('currency.js') // true