使用array.reduce计算对象数组中的出现次数

const items = [
  { name: 'apple', category: 'fruit' },
  { name: 'banana', category: 'fruit' },
  { name: 'carrot', category: 'vegetable' },
  { name: 'lettuce', category: 'vegetable' },
  { name: 'grape', category: 'fruit' }
];

const categoryCounts = items.reduce((accumulator, currentItem) => {
  // 如果累加器中已经有这个类别，则增加计数
  if (accumulator[currentItem.category]) {
    accumulator[currentItem.category]++;
  } else {
    // 否则，初始化计数为1
    accumulator[currentItem.category] = 1;
  }
  return accumulator;
}, {}); // 初始值为空对象

console.log(categoryCounts);
// 输出: { fruit: 3, vegetable: 2 }

const safeCategoryCounts = items.reduce((accumulator, currentItem) => {
  const category = currentItem.category;
  if (category && typeof category === 'string') {
    accumulator[category] = (accumulator[category] || 0) + 1;
  }
  return accumulator;
}, {});

console.log(safeCategoryCounts);