在Javascript的reduce.method中索引参数是如何工作的

array.reduce(function(accumulator, currentValue, index, array) {
  // 你的操作和计算逻辑
}, initialValue);

const arr = [1, 2, 3, 4, 5];
const sum = arr.reduce(function(accumulator, currentValue, index) {
  if (index % 2 !== 0) {
    return accumulator + currentValue;
  }
  return accumulator;
}, 0);

console.log(sum); // 输出：9，即 2 + 4 + 5

const arr = [10, 20, 30, 40, 50];
const grouped = arr.reduce(function(accumulator, currentValue, index) {
  if (index % 2 === 0) {
    accumulator.even.push(currentValue);
  } else {
    accumulator.odd.push(currentValue);
  }
  return accumulator;
}, { even: [], odd: [] });

console.log(grouped);
// 输出：{ even: [10, 30, 50], odd: [20, 40] }