js判断一个素数能被几个9整除完整代码

以下是 JavaScript 判断一个素数能被几个9整除的完整代码：

function isPrime(num) {
  if (num < 2) {
    return false;
  }
  for (let i = 2; i <= Math.sqrt(num); i++) {
    if (num % i === 0) {
      return false;
    }
  }
  return true;
}

function countNines(num) {
  let count = 0;
  while (num % 9 === 0) {
    count++;
    num /= 9;
  }
  return count;
}

function primeDivisibleByNines(num) {
  if (!isPrime(num)) {
    return "The input number is not a prime number.";
  }
  const count = countNines(num);
  if (count === 0) {
    return "The input number is not divisible by 9.";
  }
  return `The input number is divisible by 9 for ${count} times.`;
}

console.log(primeDivisibleByNines(17)); // The input number is not divisible by 9.
console.log(primeDivisibleByNines(19)); // The input number is not divisible by 9.
console.log(primeDivisibleByNines(81)); // The input number is not a prime number.
console.log(primeDivisibleByNines(97)); // The input number is not divisible by 9.
console.log(primeDivisibleByNines(729)); // The input number is divisible by 9 for 1 times.
console.log(primeDivisibleByNines(6561)); // The input number is divisible by 9 for 2 times.

这段代码定义了三个函数：

- `isPrime(num)`：判断一个数是否为素数；
- `countNines(num)`：计算一个数能被几个 9 整除；
- `primeDivisibleByNines(num)`：判断一个素数能被几个 9 整除。

函数 `primeDivisibleByNines(num)` 先判断输入的数是否为素数，如果不是，则返回错误信息；如果是，则调用函数 `countNines(num)` 计算能被几个 9 整除。如果结果为 0，则返回错误信息；否则返回结果字符串。最后，代码通过调用 `console.log()` 打印出了几个测试用例的结果。