JS Base64+rot13 algorithm SRC

<script>
function rot13(string) {
var result = '';
var str = string;
function strg(out){
    var result1 = [];
    return result1 = out.split('');
  }
  var alphArr =strg('abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ');
  var inverseArr =strg('nopqrstuvwxyzabcdefghijklmNOPQRSTUVWXYZABCDEFGHIJKL');
 for ( var i = 0; i < str.length; i++ ) {
     if (alphArr.indexOf( str[i] ) !== -1)
 {
        result += inverseArr[ alphArr.indexOf(str[i]) ];
    } else result += str[i];
  }
 return result;
}
var str=prompt('Enter Value:');
var strr=prompt('Enter Value:');
var str1=atob(str);
var str2=rot13(str)
var r=(str1+str2)
alert(r);

</script>