遍历对象统计所有数组中指定字符串的出现次数

你的代码核心问题在于遍历逻辑错误：festivals[festival]拿到的是每个用户对应的数组，直接和字符串target做全等比较永远不会成立，所以计数一直为0。要实现需求，需要先遍历对象的每个数组，再统计数组内目标字符串的出现次数并累加。

修正方案1：嵌套循环实现 #

const festivals = {
  'Danny': ['Glastonbury','Glastonbury','Leeds','Leeds','Leeds','Benicassim','MadCool'],
  'Jimbo': ['Glastonbury','Glastonbury','Leeds','Leeds','Leeds','Leeds','Benicassim','MadCool'],
  'Richard': ['Glastonbury','Leeds','Leeds','Benicassim','MadCool'],
  'John': ['Glastonbury','Leeds']
}

let totalFestivals = 0
let target = 'Benicassim'

// 遍历对象中每个用户的节日数组
for (let person in festivals) {
  const arr = festivals[person];
  // 遍历当前数组的每个元素
  for (let item of arr) {
    if (item === target) {
      totalFestivals++;
    }
  }
}
console.log(totalFestivals); // 输出3

修正方案2：用数组方法简化代码 #

利用Object.values()提取所有数组，再通过reduce和filter快速累加次数：

const festivals = {
  'Danny': ['Glastonbury','Glastonbury','Leeds','Leeds','Leeds','Benicassim','MadCool'],
  'Jimbo': ['Glastonbury','Glastonbury','Leeds','Leeds','Leeds','Leeds','Benicassim','MadCool'],
  'Richard': ['Glastonbury','Leeds','Leeds','Benicassim','MadCool'],
  'John': ['Glastonbury','Leeds']
}

const target = 'Benicassim';
const totalFestivals = Object.values(festivals).reduce((total, arr) => {
  return total + arr.filter(item => item === target).length;
}, 0);

console.log(totalFestivals); // 输出3

内容的提问来源于stack exchange，提问作者TheFall1976