對於字符串中連續出現的字母進行遞增，出現的數字進行遞減

例子：字符串124346564abcd 輸出43 65 abcd

具體實現：

str = "124346564abcd"
var num = str.match(/[0-9]/g)
var letter = str.match(/[a-z,A-Z]/g);

// let numberList = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
let numberList = [9,8,7,6,5,4,3,2,1,0]

let letterList = ['a', 'b', 'c', 'd', 'e']

// 找到第一個數字(字母)出現的位置
function findFirst(arr,num) {
  for (let index = 0; index < arr.length; index++) {
      if (arr[index] == num) { 
        return index
      }
    }
}
let startIndex = 0
if (num.length > 0) {
  // 在字典中的起始位置
   startIndex = findFirst(numberList, num[0])
}

// 數字結果
let numArr = []

// 處理數字
let indexNum = 0
function main(arr) {
  // 計數標識
  let numIndex = 0
  let result = ''
  for (let index = startIndex; index < numberList.length; index++) {
      if (numberList[index] == arr[indexNum]) {
        numIndex ++
        indexNum ++
        result += numberList[index]
      } else if (numIndex >= 2) {
        numArr.push(result)
        result = ''
        startIndex = index
        numIndex = 0
      } else { 
        startIndex = findFirst(numberList, arr[indexNum])
        result = ''
        numIndex = 0
        if (indexNum < arr.length) { 
          main(num)
        }
        break
      }
  }
}


let startIndexLetter = 0
if (letter.length > 0) {
  // 在字典中的起始位置
  startIndexLetter = findFirst(letterList, letter[0])
}
// 字母結果
let letterArr = []
// 處理字母
let indexLet = 0
function mainLetter(arr) {
  // 計數標識
  let numIndex = 0
  let result = ''
  for (let index = startIndexLetter; index < letterList.length; index++) {
    if (letterList[index] == arr[indexLet]) {
        numIndex ++
        indexLet ++
        result += letterList[index]
      } else if (numIndex >= 2) {
        letterArr.push(result)
        result = ''
        startIndexLetter = index
        numIndex = 0
    } else { 
        startIndexLetter = findFirst(letterList, arr[indexLet])
        if (indexLet < arr.length) { 
          mainLetter(letter)
        }
        break
      }
  }
}


if (num && num.length>0) { 
  main(num)
  console.log(numArr);
}

if (letter&&letter.length>0) { 
  mainLetter(letter)
  console.log(letterArr);
}

這種方法很差，各位要是有好的方法請告知