Function to convert cents into euros using regex replace

formatCents.ts

const formatCents = (sum?: number | null): string =>
  sum
    ? (sum / 100).toFixed(2).toString().replace(/\B(?=(\d{3})+(?!\d))/g, ".").replace(/\.([^.]*)$/g, ",$1")
    : '0,00';
    
  // Tests:
  
  // it('formats cents into EURO (€) values', () => {
  //   expect(formatCents(1)).toEqual('0,01');
  //   expect(formatCents(10)).toEqual('0,10');
  //   expect(formatCents(100)).toEqual('1,00');
  //   expect(formatCents(1000)).toEqual('10,00');
  //   expect(formatCents(10000)).toEqual('100,00');
  //   expect(formatCents(100000)).toEqual('1.000,00');
  //   expect(formatCents(1000000)).toEqual('10.000,00');
  //   expect(formatCents(0)).toEqual('0,00');
  //   expect(formatCents(null)).toEqual('0,00');
  //   expect(formatCents(undefined)).toEqual('0,00');
  //   expect(formatCents(0.1)).toEqual('0,00');
  //   expect(formatCents(-100)).toEqual('-1,00');
  // })