var img = document.getElementsByClassName("showcaseimg")[0];
for (i = 0; i < img.length; i++) {
    img[i].onclick = setInterval(){
    var interval;
    }
})

function setInterval() {
    img[i].style.transform="scale(2,2)";
    window.onclick = function() {
    clearInterval(interval);
        }
}, 3000);