jQuery event to trigger action when a Element is made visible

isVisible.js

jQuery(document).ready(function ($) {
 	  let alreadyThere = false;

		$.fn.isVisible = function (topSet = 0) {
			_this = $(this);
			_this = (typeof _this == 'object' || typeof _this == 'function') ? _this.get(0) : _this;
			const rect = _this.getBoundingClientRect();
      
			return (
				rect.bottom >= 0 &&
				rect.right >= 0 &&
				rect.top + topSet <= (window.innerHeight || document.documentElement.clientHeight) &&
				rect.left <= (window.innerWidth || document.documentElement.clientWidth)
			);
		};


		$(window).scroll(function () {
			if (!alreadyThere && $('.navigation.post-navigation').isVisible()) {
				alreadyThere = true;  // Perfrom action once
         /*
             Action Code
         */
			}
		});
	});