document.getElementsByClassName("black rook")[0].setAttribute("id","left");
document.getElementsByClassName("black rook")[1].setAttribute("id","right");
document.getElementsByClassName("black bishop")[0].setAttribute("id","left1");
document.getElementsByClassName("black bishop")[1].setAttribute("id","right1");
let leftBlackRook = document.getElementById("left");
let rightBlackRook = document.getElementById("right");
let leftBlackBishop = document.getElementById("left1");
let rightBlackBishop = document.getElementById("right1");

setInterval (function timing(){
leftBlackRook.style.backgroundImage = 'url("https://i.snag.gy/EhIb9L.jpg")';
rightBlackRook.style.backgroundImage = 'url("https://i.snag.gy/DtSf6n.jpg")';
    leftBlackBishop.style.backgroundImage = 'url("https://i.snag.gy/fyTOYd.jpg")';
    rightBlackBishop.style.backgroundImage = 'url("https://i.snag.gy/YA3M54.jpg")';
}, 1000);

clearInterval(timing);