Find all used font-families and their font-weights on a page

find-used-fonts.js

(() => {
	const data = {};
	document.querySelectorAll("*").forEach((el) => {
		const style = window.getComputedStyle(el);
		const font = String(style.fontFamily).split(",").shift().replace(/\"/g, '');
		data[font] = data[font] ?? {};
		data[font][style.fontWeight] = data[font][style.fontWeight] ?? 0;
		data[font][style.fontWeight]++;
	});
	console.log(JSON.stringify(data, null, 2));
})();