Checking if Font Awesome loaded

Icon fonts have become a widely-adopted visual asset on the web today and continue to grow in popularity. When your web page downloads resources — e.g., from a content delivery network (CDN) — you need to know if the HTTP request returned the files you requested. This is important whether it’s a JavaScript library, CSS framework, or in this case, icon fonts. Otherwise your icons might not load.

So let’s take a crack at it.

Not a JavaScript library

Icon font libraries, unlike JavaScript libraries, typically consist of only CSS and fonts files. Font Awesome is among the most popular of these resources, so we’ll use that for this example.

If we were getting the jQuery library we’d be able to check if the jQuery object loaded via the CDN using window.jQuery . If it didn’t load, we’d fallback to use a local copy. With Font Awesome there’s no JavaScript to detect. One way we can detect Font Awesome is by creating an element and checking if the correct CSS is applied to it.

We’ll start by adding Font Awesome to the web page:

<link rel= "stylesheet" href= "https://maxcdn.bootstrapcdn.com/font-awesome/4.6.3/css/font-awesome.min.css" >

Now let’s write a function to create a <span> element:

( function () { let span = document . createElement ( ' span ' ); })();

Note that this function will be immediately-invoked. Next we’ll add a CSS class to the <span> :

( function () { let span = document . createElement ( ' span ' ); span . className = ' fa ' ; span . style . display = ' none ' ; })();

The .fa class is the default class name used by Font Awesome. We also don’t want the <span> to be visible so we’ve added display: none as an inline style on the element.

Let’s add the <span> as the first element of the <body> :

( function () { let span = document . createElement ( ' span ' ); span . className = ' fa ' ; span . style . display = ' none ' ; document . body . insertBefore ( span , document . body . firstChild ); })();

The .fa class has a font-family value of FontAwesome . This will be what we check to validate if the Font Awesome library loaded.

Reading the computed style

In order to be able to read the font-family property we need a way to get the values of the <span> . The getComputedStyle() method will return all CSS values of an element, which is perfect for what we’re doing.

So let’s go ahead and create a function to get the computed style:

function css ( element , property ) { return window . getComputedStyle ( element , null ). getPropertyValue ( property ); }

The function will be passed the element and CSS property. We’ll add this as an inner function to the function we’ve already created:

( function () { let span = document . createElement ( ' span ' ); span . className = ' fa ' ; span . style . display = ' none ' ; document . body . insertBefore ( span , document . body . firstChild ); function css ( element , property ) { return window . getComputedStyle ( element , null ). getPropertyValue ( property ); } })();

Let’s run our check for Font Awesome in an if statement:

( function () { let span = document . createElement ( ' span ' ); span . className = ' fa ' ; span . style . display = ' none ' ; document . body . insertBefore ( span , document . body . firstChild ); function css ( element , property ) { return window . getComputedStyle ( element , null ). getPropertyValue ( property ); } if ( css ( span , ' font-family ' ) !== ' FontAwesome ' ) { let headHTML = document . head . innerHTML ; headHTML += ' <link rel="stylesheet" href="third-party/font-awesome/css/font-awesome.min.css"> ' ; document . head . innerHTML = headHTML ; } document . body . removeChild ( span ); })();

If the font-family isn’t FontAwesome we’ll add a local copy of the library to the <head> . Lastly, now that we’ve performed the check we’ll remove the <span> element from the <body> at the end of the function.

Wrapping up

Whether or not you use icon fonts is up to you. If you are and opt to serve your resource via a CDN, you’ll want to know that the resource loaded. Now you have a way tell and can similarly apply this technique to other icon font libraries.