【JS】统计字符出现次数

现有一字符，要求统计每一个字符出现次数。

let str = "cbdbadcacbbdbacac"

遍历

let str = "cbaddacbc"
let res = {}
for (let i = 0; i < str.length; i++) {
  if (res[str[i]]) {
    res[str[i]]++
  } else {
    res[str[i]] = 1
  }
}
console.log(res);  // {c: 3, b: 2, a: 2, d: 2}

reduce

const result = str.split("").reduce((acc, current) => {
  if (acc[current]) {
    acc[current]++
  } else {
    acc[current] = 1
  }
  return acc
}, {})
console.log(result); // {c: 3, b: 2, a: 2, d: 2}

代码可简化为：

const result = str.split("").reduce((acc, current) => {
  acc[current]++ || (acc[current] = 1)
  return acc
}, {})

由于return只返回最后一个变量，具体可看另一篇文章return a,b，所以可继续简化为：

const result = str.split("").reduce((acc, current) => {
  return (acc[current]++ || (acc[current] = 1),acc)
}, {})

// 省略return
const result = str.split("").reduce((acc, current) => (acc[current]++ || (acc[current] = 1), acc), {})