save-data.html

<!doctype html>
<html lang="en">
<head>
	<meta charset="utf-8">
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<title>FOUT with Save-Data</title>
	<style>
	body {
		font-family: Lato, sans-serif;
	}
	
	</style>
	<script>
	(function() {
		function loadFonts() {
			if( !("fonts" in document ) ) {
				return;
			}

			var fontRoman = new FontFace("Lato", "url('font-lato/lato-regular-webfont.woff2') format('woff2'),url('font-lato/lato-regular-webfont.woff') format('woff')");
			var fontBold = new FontFace("Lato", "url('font-lato/lato-bold-webfont.woff2') format('woff2'),url('font-lato/lato-bold-webfont.woff') format('woff')", {
				weight: "700"
			});
			var fontItalic = new FontFace("Lato", "url('font-lato/lato-italic-webfont.woff2') format('woff2'),url('font-lato/lato-italic-webfont.woff') format('woff')", {
				style: "italic"
			});
			var fontBoldItalic = new FontFace("Lato", "url('font-lato/lato-bolditalic-webfont.woff2') format('woff2'),url('font-lato/lato-bolditalic-webfont.woff') format('woff')", {
				weight: "700",
				style: "italic"
			});

			Promise.all([
				fontRoman.load(),
				fontBold.load(),
				fontItalic.load(),
				fontBoldItalic.load()
			]).then(function(loadedFonts) {

				// Render them at the same time
				loadedFonts.forEach(function(font) {
					document.fonts.add(font);
				});
			});
		}

		if( navigator.connection && navigator.connection.saveData ) {
		} else {
			loadFonts();
		}
	})();
	</script>
</head>
<body>
	<h1>FOUT with Save-Data</h1>
	<p>This is a paragraph. <strong>This is heavier text.</strong> <em>This is emphasized text.</em> <strong><em>This is heavier and emphasized text.</em></strong></p>

	<hr style="margin-top: 2em">
	<ul>
		<li>This demo is a companion to <a href="https://www.zachleat.com/web/comprehensive-webfonts/">A Comprehensive Guide to Font Loading Strategies</a></li>
		<li>See all demos on <a href="https://github.com/zachleat/web-font-loading-recipes">GitHub <code>zachleat/web-font-loading-recipes</code></a></li>
	</ul>
</body>
</html>