var skinIndex = -1;

function swapSkins() {
    skinIndex *= -1;

    var blues = Array.from(document.getElementsByClassName("skin-blue"));
    var reds = Array.from(document.getElementsByClassName("skin-red"));

    if(skinIndex > 0) {
        blues.forEach(element => {
            element.style.display = "none";
        });
        reds.forEach(element => {
            element.style.display = "initial";
        });
    }
    else {
        blues.forEach(element => {
            element.style.display = "initial";
        });
        reds.forEach(element => {
            element.style.display = "none";
        });
    }
}

swapSkins();

setInterval(() => {
    swapSkins();
}, 1000 * 1); //1 seconds