var allDivs = document.getElementsByTagName('div');

var c = 0;

function next() {
    c = c + 1;
    c = c % allDivs.length;
    return allDivs[c];
}

function prev() {
    if (c === 0) {
        c = allDivs.length;
    }
    c = c - 1;
    return allDivs[c];
}

function checkKey(e) {
    e = e || window.event;

    // J
    if (e.keyCode == 74) {
        var current = allDivs[c];
        current.classList.remove('active');
        var p = prev();
        p.classList.add('active');
    }
    else if (e.keyCode == 75) {
        var current = allDivs[c];
        current.classList.remove('active');
        var n = next();
        n.classList.add('active');
    }
    else if (e.keyCode == 67) {
        for (var i = 0; i < allDivs.length; i++) {
            allDivs[i].classList.remove('active');
        }
    }
}

document.onkeydown = checkKey;