godot-docs/_extensions/sphinx_tabs/tabs.js

// From http://stackoverflow.com/questions/123999/how-to-tell-if-a-dom-element-is-visible-in-the-current-viewport
function elementIsInView (el) {
  if (typeof jQuery === "function" && el instanceof jQuery) {
    el = el[0];
  }

  const  rect = el.getBoundingClientRect();

  return (
    rect.top >= 0 &&
    rect.left >= 0 &&
    rect.bottom <= (window.innerHeight || document.documentElement.clientHeight) &&
    rect.right <= (window.innerWidth || document.documentElement.clientWidth)
  );
}

$(function() {
  // Change container tags <div> -> <a>
  $('.sphinx-menu.menu .item').each(function() {
    var this_ = $(this);
    var a_this = $('<a>');

    a_this.html(this_.html());
    $.each(this_.prop('attributes'), function() {
      a_this.attr(this.name, this.value);
    });

    this_.replaceWith(a_this);
  });

  // We store the data-tab values as sphinx-data-<data-tab value>
  // Add data-tab attribute with the extracted value
  $('.sphinx-menu.menu .item, .sphinx-tab.tab').each(function() {
    var this_ = $(this);
    const prefix = 'sphinx-data-';
    const classes = this_.attr('class').split(/\s+/);
    $.each(classes, function(idx, clazz) {
      if (clazz.startsWith(prefix)) {
        this_.attr('data-tab',
                   clazz.substring(prefix.length));
      }
    });
  });

  // Mimic the Semantic UI behaviour
  $('.sphinx-menu.menu .item').each(function() {
    var this1 = $(this);
    var data_tab = this1.attr('data-tab');

    this1.on('click', function() {
      // Find offset in view
      const offset = (this1.offset().top - $(window).scrollTop());

      $('[data-tab]').each(function() {
        var this2 = $(this);
        // Remove 'active' class from tabs that aren't the same
        if (this2.attr('data-tab') !== data_tab) {
          // Keep 'active' if there isn't a tab with the same data-tab value
          if (0 < this2.parent().find('[data-tab="' + data_tab + '"]').length) {
            this2.removeClass('active');
          }
        } else {
          // Add 'active' if data-tab value is the same
          this2.addClass('active');
        }
      });

      // Keep tab with the original view offset
      $(window).scrollTop(this1.offset().top - offset);
    });
  });
});