sncf/templates/assets/index.js

// csrf_token is retrieved from server-side template
document.getElementById('new_link_button').addEventListener('click', function () {
    new_link(csrf_token);
});

function new_link(csrf) {
    document.getElementById("csrf_token").value = csrf;
    document.getElementById('new_link').submit();
    document.getElementById('new_link_button').classList.add("hidden");
    document.getElementById('loading_ring').classList.remove("hidden");
}