返回长度为n的随机数字符串的函数

function nRandom(n) {
  let max = 1
  for (let i = 0; i < n; i++) {
    max *= 10
  }
  let str = '' + parseInt(Math.random() * max)
  let count = n - str.length
  for (let j = 0; j < count; j++) {
    str += '0'
  }
  return str
}