如何用函数式将字符串中的位数相加到特定的索引

// 定义一个函数，用于计算字符的位数
const getDigitCount = (char) => {
  const num = parseInt(char);
  return num.toString().length;
};

// 定义一个函数，用于将字符串中特定索引位置的字符的位数相加
const sumDigitsAtIndex = (str, index) => {
  if (index < 0 || index >= str.length) {
    throw new Error('Index out of bounds');
  }

  const char = str[index];
  return getDigitCount(char);
};

// 示例
const inputStr = 'a1b2c3d4';
const targetIndex = 2; // 我们想要计算索引为2的字符（'c'）的位数之和
const result = sumDigitsAtIndex(inputStr, targetIndex);

console.log(`The sum of digits at index ${targetIndex} is: ${result}`); // 输出：The sum of digits at index 2 is: 1

const sumAllDigits = (str) => {
  return str.split('').reduce((sum, char) => {
    if (!isNaN(char)) {
      return sum + getDigitCount(char);
    }
    return sum;
  }, 0);
};

const inputStr = 'a1b2c3d4';
const result = sumAllDigits(inputStr);

console.log(`The sum of all digits in the string is: ${result}`); // 输出：The sum of all digits in the string is: 4