Pass several variables by cookies from JavaScript to PHP

I am trying to pass several variables per cookie from javascript to php, but I get that they are undefined. If I try to pass only one variable, if it works, I guess I'll have to treat it as an array, but I do not know how to handle it.

JavaScript

function modificarFormacion()
{
    var tipo = document.getElementById("tipo");
    var categoria = document.getElementById("categoria");

    document.cookie = "tipo="+tipo.value;
    document.cookie = "categoria="+categoria.value;
}

PHP

 <?php
    $tipo = $_COOKIE['valor'];
    $categoria = $_COOKIE['categoria'];
    echo $tipo;
    echo $categoria;    
?>

If I do it only with type or with category, if I show in PHP the value of the variable.

How can I solve the problem of passing variable variables from JavaScript to PHP?