text: const array1 = [1, 2, 3, 4];
  const reducer = (previousValue, currentValue) => previousValue + currentValue;
  
  // 1 + 2 + 3 + 4
  console.log(array1.reduce(reducer));
  // saída experada: 10
  
  // 5 + 1 + 2 + 3 + 4
  console.log(array1.reduce(reducer, 5));
  // saída experada: 15
  