如何使用JavaScript统计Phone模式提醒的总数量？

原始数据 #

const coachData = [
  {
    "coachName": "Angela",
    "coachId": 94253,
    "reminders": [
      { "day": "Tuesday", "mode": "Text" },
      { "day": "Tuesday", "mode": "Phone" },
      { "day": "Tuesday", "mode": "Text" },
      { "day": "Tuesday", "mode": "Text" },
      { "day": "Tuesday", "mode": "Text" },
      { "day": "Tuesday", "mode": "Phone" },
      { "day": "Wednesday", "mode": "Text" },
      { "day": "Wednesday", "mode": "Text" },
      { "day": "Wednesday", "mode": "Text" },
      { "day": "Wednesday", "mode": "Text" },
      { "day": "Wednesday", "mode": "Text" }
    ]
  },
  {
    "coachName": "Melanie",
    "coachId": 94254,
    "reminders": [
      { "day": "Wednesday", "mode": "Phone" },
      { "day": "Wednesday", "mode": "Text" },
      { "day": "Wednesday", "mode": "Phone" },
      { "day": "Monday", "mode": "Text" },
      { "day": "Monday", "mode": "Phone" },
      { "day": "Monday", "mode": "Text" },
      { "day": "Monday", "mode": "Text" },
      { "day": "Monday", "mode": "Text" },
      { "day": "Monday", "mode": "Phone" },
      { "day": "Monday", "mode": "Text" }
    ]
  }
];

解法一：forEach循环累加 #

初始化计数器，逐层遍历教练列表和对应提醒，判断模式为Phone时累加计数：

let phoneCount = 0;

coachData.forEach(coach => {
  coach.reminders.forEach(reminder => {
    if (reminder.mode === 'Phone') {
      phoneCount++;
    }
  });
});

console.log(phoneCount); // 输出：6

解法二：reduce链式调用 #

先用reduce合并所有教练的提醒数组，再通过reduce统计符合条件的数量，写法更简洁：

const phoneCount = coachData
  .reduce((acc, coach) => acc.concat(coach.reminders), [])
  .reduce((count, reminder) => {
    return reminder.mode === 'Phone' ? count + 1 : count;
  }, 0);

console.log(phoneCount); // 输出：6

解法三：flatMap + filter 组合 #

用flatMap提取所有提醒项，再筛选出模式为Phone的条目，最终取数组长度得到总数：

const phoneCount = coachData
  .flatMap(coach => coach.reminders)
  .filter(reminder => reminder.mode === 'Phone').length;

console.log(phoneCount); // 输出：6

内容的提问来源于stack exchange，提问作者Saranya