Answer 1

function push (arr, item) {
arr[arr.length] = item;
}

Answer 2

function getRepetCount(str) {
    let maxChars = '';
    let maxCount = 0;
    let length = str.length;
    let count = 1;
    for (let index = 1; index < length; index++) {
        const cur = str[index];
        const pre = str[index - 1];
        if (cur === pre) {
            count++;
        } else {
            if (count > maxCount) {
                maxCount = count;
                maxChars = pre;
            }
            count = 1;
        }
    }
    return {
        [maxChars]: maxCount
    }
}

Answer 3

@hellobabyting

var fs = require('fs')

// callback usage
fs.readdir('./', function (err, files) {
  ...
})

// promisify
let promisifyReadDir = promisify(fs.readdir)
promisifyReadDir('./').then(files => {
  console.log(files)
})

Answer 4

@alanchanzm 1. class 声明会提升 . 是不是写错了?
原文: Class declarations, unlike function declarations, are not hoisted.