Generate password random JS/PHP

passwordRand.js

#JS
function generatePasswordRand(length,type) {
    switch(type){
        case 'num':
            characters = "0123456789";
            break;
        case 'alf':
            characters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
            break;
        case 'rand':
            //FOR ↓
            break;
        default:
            characters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
            break;
    }
    var pass = "";
    for (i=0; i < length; i++){
        if(type == 'rand'){
            pass += String.fromCharCode((Math.floor((Math.random() * 100)) % 94) + 33);
        }else{
            pass += characters.charAt(Math.floor(Math.random()*characters.length));
        }
    }
    return pass;
}

#PHP
//Generar una contraseña aleatoria
function generatePassword($longitud = 6,$tipo = ''){
  switch ($tipo) {
    case 'num':
        $cadena="/\D+/";
      break;
    case 'alf':
        $cadena="/\d+/";
      break;
    default:
        $cadena="/\W+/";
      break;
  }
  return substr(preg_replace($cadena, "", md5(rand())).preg_replace($cadena, "", md5(rand())).preg_replace($cadena, "", md5(rand())), 0, $longitud);
}