gistfile1.js

// Page 3

document.addEventListener('DOMContentLoaded', function init() {

	var testD = document.querySelector('#testDetails');
	var summary = testD.querySelector('summary');

	summary.addEventListener('click', function () {
		var open = !testD.hasAttribute('open');
		console.log(open);
	}, false);	

});


// Page 4

$(function () {
	
	var testD = $('#testDetails');
	var summary = $('summary', testD);

	summary.on('click', function () {
		var open = !testD.attr('open');
		var loaded = testD.data('loaded');
		var url;

		if (open && !loaded) {
			testD.data('loaded', true);
			url = testD.data('details');
			$.get(url).then(function (res) {
				$(summary).after(res);
			});
		}
	});
	
});

testing gist notifications, but everything is wrong in this 2013 gist anyway :D (take this with hirony)

• tabs are disturbing
• addEventListener('DOMContentLoaded', ...) works too, no need to use document
• the global selector, since there is an ID involved, is a bit LOL, 'cause any ID is reflected in the window object, so that testDetails would be already available
• jQuery is disturbing in 2019