Prestashop 1.6 encrypt password can't reproduce the encryption in nodejs

Question

I try to reproduce the hash of prestashop's password with nodejs and I find a difference in php.

<?php 
define(_COOKIE_KEY_, 'foo');
$pass = 'bar';

$hash1 = md5(_COOKIE_KEY_ . $pass);
$hash2 = md5('foo' . $pass);

// $hash1 !== $hash2

In NodeJS (with md5 module) I found only the $hash2 but impossible to find $hash1.

Someone know why ? and how to reproduce ?

Thanks a lot.