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The deferred font loading logic for Smashing Magazine. http://www.smashingmagazine.com/
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<script type="text/javascript"> | |
(function () { | |
"use strict"; | |
// once cached, the css file is stored on the client forever unless | |
// the URL below is changed. Any change will invalidate the cache | |
var css_href = './index_files/web-fonts.css'; | |
// a simple event handler wrapper | |
function on(el, ev, callback) { | |
if (el.addEventListener) { | |
el.addEventListener(ev, callback, false); | |
} else if (el.attachEvent) { | |
el.attachEvent("on" + ev, callback); | |
} | |
} | |
// if we have the fonts in localStorage or if we've cached them using the native batrowser cache | |
if ((window.localStorage && localStorage.font_css_cache) || document.cookie.indexOf('font_css_cache') > -1){ | |
// just use the cached version | |
injectFontsStylesheet(); | |
} else { | |
// otherwise, don't block the loading of the page; wait until it's done. | |
on(window, "load", injectFontsStylesheet); | |
} | |
// quick way to determine whether a css file has been cached locally | |
function fileIsCached(href) { | |
return window.localStorage && localStorage.font_css_cache && (localStorage.font_css_cache_file === href); | |
} | |
// time to get the actual css file | |
function injectFontsStylesheet() { | |
// if this is an older browser | |
if (!window.localStorage || !window.XMLHttpRequest) { | |
var stylesheet = document.createElement('link'); | |
stylesheet.href = css_href; | |
stylesheet.rel = 'stylesheet'; | |
stylesheet.type = 'text/css'; | |
document.getElementsByTagName('head')[0].appendChild(stylesheet); | |
// just use the native browser cache | |
// this requires a good expires header on the server | |
document.cookie = "font_css_cache"; | |
// if this isn't an old browser | |
} else { | |
// use the cached version if we already have it | |
if (fileIsCached(css_href)) { | |
injectRawStyle(localStorage.font_css_cache); | |
// otherwise, load it with ajax | |
} else { | |
var xhr = new XMLHttpRequest(); | |
xhr.open("GET", css_href, true); | |
// cater for IE8 which does not support addEventListener or attachEvent on XMLHttpRequest | |
xhr.onreadystatechange = function () { | |
if (xhr.readyState === 4) { | |
// once we have the content, quickly inject the css rules | |
injectRawStyle(xhr.responseText); | |
// and cache the text content for further use | |
// notice that this overwrites anything that might have already been previously cached | |
localStorage.font_css_cache = xhr.responseText; | |
localStorage.font_css_cache_file = css_href; | |
} | |
}; | |
xhr.send(); | |
} | |
} | |
} | |
// this is the simple utitily that injects the cached or loaded css text | |
function injectRawStyle(text) { | |
var style = document.createElement('style'); | |
// cater for IE8 which doesn't support style.innerHTML | |
style.setAttribute("type", "text/css"); | |
if (style.styleSheet) { | |
style.styleSheet.cssText = text; | |
} else { | |
style.innerHTML = text; | |
} | |
document.getElementsByTagName('head')[0].appendChild(style); | |
} | |
}()); | |
</script> |
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