const fake_limit = 1_000;
const fake_array = Array(fake_limit);

{
    console.time('unshift-length');

    for (let offset = 0; offset <= 1_000_000; ++offset)
    {
        fake_array.unshift(offset);
        fake_array.length = fake_limit;
    }

    console.timeEnd('unshift-length');
};

{
    console.time('push-splice');

    for (let offset = 0; offset <= 1_000_000; ++offset)
    {
        const new_len = fake_array.push(offset);
        const removes = new_len - fake_limit;

        if (removes > 0)
        {
            fake_array.splice(0, removes);
        }
    }

    console.timeEnd('push-splice');
};