[Nexus]

$('.checkshadow3').click(function() {
    const originalSrcDataPropertyName = 'original-src';
    const $this = $(this).find('img');
    if ($this.data(originalSrcDataPropertyName))
        return void $this
            .attr('src', $this.data(originalSrcDataPropertyName))
            .removeData(originalSrcDataPropertyName);

    let source = $this.attr('src').split('?').shift().split('/').pop();
    let src = source.split('.');
    src[0] += '_a';
    src = src.join('.');

    $this
        .data(originalSrcDataPropertyName, $this.attr('src'))
        .attr('src', $this.attr('src').replace(source, src));
});