相信平时书写代码中一定会遇到需要统计字符出现次数的

普通版

       let st = 'daaadahsdahsdgywawahdshahdgahgdadahdgadg'
        let aaa = {}
        for (let i = 0; i < st.length; i++) {
            if (aaa[st[i]]) {
                aaa[st[i]]++
            } else {
                aaa[st[i]] = 1
            }
        }
        console.log(aaa);

结果：{d: 10, a: 12, h: 7, s: 3, g: 5, …}

升级版

         let st = 'daaadahsdahsdgywawahdshahdgahgdadahdgadg'        
         let sum = st.split('').reduce((total, item) => {
            if (total[item]) {
                total[item]++
            } else {
                total[item] = 1
            }
            return total
        }, {})
        console.log(sum);

最终升级版

        let st = 'daaadahsdahsdgywawahdshahdgahgdadahdgadg'

        let sum = st.split('').reduce((total, item) => {
            total[item]++ || (total[item] = 1)
            return total
        }, {})
        console.log(sum);

total[item]++第一次没有为Nan，Nan在判断力为false