Enabling fonts when they’re really loaded to 'Enabling fonts when they’re really loaded' #Īfter realizing that even data URIs can introduce a FOIT while they’re being parsed, we wanted to ensure that we applied our fonts to the page only after they were truly ready to render. Interestingly enough, in this case it appeared that although the CSS and its included fonts had indeed already been delivered over the network to the browser, the browser still seemed to hide the text while parsing the data URI string, which we know can take a little time, particularly on slower devices. In short, a FOIT happens when a browser attempts to style an HTML element with a font-family that is defined (via a declaration) but not yet loaded. But the characteristic hidden text alongside visible graphic elements sure looked like your run-of-the-mill FOIT, and sure enough, it was. Finding the source of the problem to 'Finding the source of the problem' #Īt first we wondered if the blink was just an artifact of repainting/reflowing a moderately complex layout. Something was up, and it seemed we had a little more work to do. And we sometimes saw longer delays of 500ms or so on client sites that were utilizing more custom fonts than our site does. So another 100ms of hidden text still isn’t terrible, but it was certainly odd. For example, here’s the same load on 3G:įIG 3: Timeline of our website using async-loaded data URI fonts. Of course, 800ms is a very fast page load, and a 100ms blink may not be the end of the world, but we found that the problem tended to display more prominently on slower connections and devices and on other sites as well. Looking at the request timing, we could see that the FOIT began just after the fonts finished loading. In this timeline, the page is usable (with fallback fonts) at around 600ms, but then for about 100ms, a FOIT occurs before the page ultimately returns to a usable state at 800ms. The page loading timeline below of our site accessed over a fast connection while using this approach displays this peculiar blip.įIG 2: Timeline of our website using async-loaded data URI fonts. It didn’t seem to happen all the time, but we’d been seeing it crop up more and more regularly. That approach seemed to serve us well, but we recently started noticing that sites using this particular approach sometimes exhibited a small side effect: a brief FOIT or blink that happens long after the fonts finish loading, just before they are applied to the page. An unexpected side effect to 'An unexpected side effect' # By loading that CSS file in an asynchronous manner (using a bit of JavaScript), we could ensure that a browser would immediately render the text in the page using fallback fonts, and the custom fonts would apply once the CSS finished loading. Our initial approach to working around the FOIT involved converting font files into Data URIs so that those fonts could be embedded directly into font-face definitions in a CSS file. A workable workaround to 'A workable workaround' # But again, that browser’s behavior is by far the worst. Since a page typically requires text to be usable, FOIT timeouts are a concern across most browsers, not just iOS Safari. After all, the performance community tends to agree that 1 second is a reasonable goal for rendering a usable page on a fast connection, and we tend to shoot for rendering something useful in 2 seconds on slower devices on mobile networks as well. It’s nice that these browsers limit their text hiding to 3 seconds, but even 3 seconds is a long time to wait for content that’s already downloaded. For example, here’s how our site would load in Chrome on a 3G-ish connection if we were loading fonts in a standard way through CSS Note that the page content is available for rendering at around 1.7 seconds in the timeline, yet the text is hidden until fonts have finished loading.įIG 1: Timeline of our website using standard custom font loading. The FOIT tends to be most problematic in browsers like iOS Safari, which hides text for up to 30 seconds before giving up and rendering it with a default font, but it can also be seen in browsers with shorter hiding durations like Chrome, Firefox, and Opera as well. A brief recap on the FOIT to 'A brief recap on the FOIT' # The purpose of the approach was to avoid a typically undesirable browser behavior we often refer to as the “FOIT” (Flash of Invisible Text), in which a browser hides all text that should be styled with a custom font until that font has finished loading. Last month we wrote about an approach we’d been using to load web fonts in a more responsible manner than browsers tend to do by default. It was formerly called “Font Loading Revisited with Font Events.” Note: This article’s title was updated for clarity.
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