JS实现逢Z进A

function getVersion(old){
 var chZ = 'Z';
 var oldChs = old.split('');
 for(var i = old.length-1;i>-1;i--){
  if(old.charCodeAt(i)==chZ.charCodeAt(0)){
   return charZ(old,oldChs,i);
  }else{
   if(old.length>0){
    oldChs[old.length-1]=String.fromCharCode(old.charCodeAt(i)+1);
    return oldChs.join('');
   }
  }
 }
}
function charZ(old,oldChs,i){
 var chA = 'A';
 var chZ = 'Z';
 oldChs[i] = chA;
 if(old.charCodeAt(i-1)==chZ.charCodeAt(0)){
  return charZ(old,oldChs,i-1);
 }else{
  if(i>0){
   oldChs[i-1] = String.fromCharCode(old.charCodeAt(i-1)+1);
   return oldChs.join('');
  }
 }
}