const pics = document.querySelectorAll('.lightGallery > li > img');

function toggleBig(test){

  var currentimg = test.src;
  //console.log(test);
  currentimg = currentimg.toString();
  currentimg = currentimg.split("_").pop();
  console.log(currentimg);
  test.parentNode.parentNode.parentNode.firstChild.nextElementSibling.src = "../_" + currentimg;
}
$(".lightGallery > li > img").on("click", function() {
  toggleBig(this);
});