Arrays & Array Methods (map, filter, reduce)

const data = [1, 2, 3, 4, 5];
const result = data.reduce((acc, curr) => {
  return curr % 2 === 0 ? acc + curr : acc;
}, 0);

The sum of all numbers
The sum of even numbers
This reduce operation calculates the sum of even numbers: 1) Initial accumulator value is 0, 2) For each number, checks if it's even using modulo, 3) If even, adds to accumulator; if odd, returns accumulator unchanged, 4) Processes array left to right, accumulating only even values, 5) More efficient than filter().reduce() combination, 6) Combines filtering and reduction in one pass, 7) Common pattern for selective accumulation, 8) Result will be sum of 2 and 4, which is 6.
The count of even numbers
The product of even numbers