How to hide part of the gallery of pictures in the spoiler?

Question

JavaScript

Greetings! There is a site on wordpress with the NextGEN Gallery plugin installed. I want to make it so that the first 2 photos from the gallery are displayed, and the rest are hidden, and by clicking on the button the list is opened?
writing in crypto

window.addEventListener("load", function() {
  var height = $('.slideshowlink').height() + $('#ngg-image-0').height() * 2;
  var button = $('<button></button>');
  var gallery = $('.ngg-galleryoverview')
  button.html('Показать все').attr('type', 'button').css({
    position: 'absolute',
    top: 0,
    right: 0
  });
  button.prependTo(gallery);
  gallery.height(height);
  button.on('click', function() {
    gallery.css('height', 'auto')
  });
});

but, through the console, you can see that $('#ngg-image-0').height() cannot determine, because gallery not loaded yet