var previousIndex = undefined;

function onClickScreenshot(index) {
    if (previousIndex !== undefined) {
        document.getElementById(`ss${previousIndex}`).className = 'screenshot';
    }

    if (previousIndex !== index) {
        var element = document.getElementById(`ss${index}`);
        element.className = 'screenshot screenshot--large';
        element.scrollIntoView();

        previousIndex = index;
    } else {
        previousIndex = undefined;
    }
}