;
        await Promise.resolve();
        assert_array_equals(reactions, ["disconnected"]);
    }, "When connectedCallback is not defined, no crash");

    promise_test(async t => {
        const ce = document.getElementById("ce");
        let reactions = [];
        const element_name = unique_element_name();
        customElements.define(element_name,
            class MockCustomElement extends HTMLElement {
                connectedCallback() { reactions.push("connected"); }
            });
        cons