递归-倒序字符串

function reverseString(str,len,strOut){
  if(len<0)return strOut //终止条件
  strOut += str.charAt(len--)
  return reverseString(str,len,strOut)
}
let str = 'abcdefg'
let result = ''
let newStr = reverseString(str,str.length-1,result)
console.log(newStr)