Click on links to see spinner on load image.

function changeImg(url) {
    var img = document.getElementById('previewImg');
    var spinner = document.getElementById('spinner');
    // show spinner
    spinner.style.display = '';
    img.style.display = 'none';
    img.onload = function() {
        spinner.style.display = 'none';
        this.style.display = '';
        this.onload = null;
    }
    img.src = url;
}