[рони]

kolobku_xxx,

function slider() {
    var blocks = document.querySelectorAll(".slide"),
        len = blocks.length,
        i = 0;

    function hello() {
        blocks[i].classList.toggle("active");
        i++;
        i %= len;
        blocks[i].classList.toggle("active");
        setTimeout(hello, 5E3)
    }
    setTimeout(hello, 5E3)
}
window.addEventListener("load", slider);