8.返回纯大写字母

      var returnCode = function(str) {
        var code = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
        var code1= 'abcdefghijklmnopqrstuvwxyz'
        var restult = ''
        for (var i = 0; i < str.length; i++) {
          var a = str[i]
          var index = code1.indexOf(a)
          //判断是否存在
          if(index>-1) {
            restult+=code[index]
          } else {
              restult+=a
          }
        }
        //返回结果
        return restult
      }