Sending JavaScript array to Php with ajax not working

I am trying to send the content of a JavaScript array to a different page using $.post, but it doesn’t work – the coreresponding $_POST is not set…

Can someone explain me what’s wrong ?

Here is the js code, on page 1:

<script type="text/javascript">
    var i = sessionStorage.length;
    var categoriesTab = [];
    for (let j = 0; j < i; j++) {
        if (sessionStorage.getItem(sessionStorage.key(j)) == 'active') {
            categoriesTab.push(sessionStorage.key(j));
        }
    }
    const liste = document.getElementById('liste');
    liste.addEventListener('click', function (event){
        event.preventDefault();
        if (window.location.href == 'https://dom.fr/page1/'){
            $.post(
                'page2.php',
                {
                    categoriesActives : categoriesTab
                }
            )
        }
        window.location.assign('https://dom.fr/page2/');
    });
</script>

The categoriesTab variable is set and everything seems to work.
But when I get to page 2, $_POST is empty… :

<?php

$array = [];

if (isset($_POST['categoriesActives'])) {
    $array = $_POST['categoriesActives'];
} else {
    $array = ['a', 'z', 'e', 'r'];
}

?>```