PHP rot5 javascript等价吗？

I am wondering if there is a rot5 function for PHP equalivant too

function rot5(str) {
  var s = [];
  for (i = 0; i < str.length; i ++)
  {
    idx = str.charCodeAt(i);
    if ((idx >= 48) && (idx <= 57))
    {
      if (idx <= 52)
      {
        s[i] = String.fromCharCode(((idx + 5)));
      }
      else
      {
        s[i] = String.fromCharCode(((idx - 5)));
      }
    } 
    else
    {
      s[i] = String.fromCharCode(idx);
    }
  }
  return s.join('');
}

In javascript? If not then how can I do fromCharCode and charCodeAt in PHP?

Here you got generic strrot with default to strrot5

<?php

function strrot($str, $n=5){
    $replace = [];
    for($i=0;$i<26;$i++){
        $replace[chr(65+$i)] = chr(65+(($i+$n)%26));
        $replace[chr(97+$i)] = chr(97+(($i+$n)%26));
    }
    return strtr($str, $replace);
}

You can use 'ord' for 'charCodeAt'.

ord($yourstring[$yourindex])

You can use 'chr' for 'fromCharCode'

chr($yourcharcode)