表格列名转序号

// 'AM' => '39'
function codeToNum(code) {
  const arr = code.toLowerCase().split('')
  let num = 0
  for (var i = 0; i < arr.length; i++) {
    num += (arr[i].charCodeAt(0) - 96) * Math.pow(26, arr.length - i - 1)
  }
  return num
}

// '39' => 'AM'
function numToCode(num) {
  const arr = []
  const recurse = nnum => {
    var num = nnum - 1
    var a = parseInt(num / 26)
    var b = num % 26
    arr.push(String.fromCharCode(64 + parseInt(b + 1)))
    if (a > 0) {
      recurse(a)
    }
  }
  recurse(num)
  return arr.reverse().join('')
}