我尝试用Javascript实现Luhns算法，但我的程序总是无限循环

function luhnsAlgorithm(number) {
  let sum = 0;
  let isDouble = false;

  for (let i = number.length - 1; i >= 0; i--) {
    let digit = parseInt(number.charAt(i));

    if (isDouble) {
      digit *= 2;
      if (digit > 9) {
        digit -= 9;
      }
    }

    sum += digit;
    isDouble = !isDouble;
  }

  return sum % 10 === 0;
}

let number = "1234567890123456";
console.log(luhnsAlgorithm(number));

function luhnsAlgorithm(number) {
  let sum = 0;
  let isDouble = false;

  for (let i = number.length - 1; i >= 0; i--) {
    let digit = parseInt(number.charAt(i));

    if (isDouble) {
      digit *= 2;
      if (digit > 9) {
        digit -= 9;
      }
    }

    sum += digit;
    isDouble = !isDouble;
  }

  return sum % 10 === 0;
}

let number = "1234567890123456";
console.log(luhnsAlgorithm(number));