loadCSS
A function for loading CSS asynchronously
[c]2014 @scottjehl, Filament Group, Inc.
Licensed MIT
Usage
Place the loadCSS
function inline in the head
of your page (it can also be included in an external JavaScript file if preferable).
Then call it by passing it a stylesheet URL:
<head>
...
<script>
function loadCSS( href, before, media ){ ... }
loadCSS( "path/to/mystylesheet.css" );
</script>
<noscript><link href="path/to/mystylesheet.css" rel="stylesheet"></noscript>
...
</head>
Optional Arguments
before
: By default, your stylesheet will be inserted before the first script
tag in the DOM (which may be the one shown above). This is risky because users' browser extensions can place scripts in the head
of your page and unintentionally change the insertion point for the CSS, which can mess up your intended CSS cascade. If possible we recommend, using the optional before
argument to specify a particular element to use as an insertion point. The stylesheet will be inserted before the element you specify. For example, here's how that can be done by simply applying an id
attribute to your script
.
...
...
```
media
: You can optionally pass a string to the media argument to set the media=""
of the stylesheet - the default value is all
.callback
(deprecated): pass an onload callback. Instead of using this callback, we recommend binding an onload handler to the returned link
element by using the onloadCSS
function in this repo.
Using with onload
Include onloadCSS
function on your page.
function onloadCSS( ss, callback ){ ... }
var stylesheet = loadCSS( "path/to/mystylesheet.css" );
onloadCSS( stylesheet, function() {
console.log( "Stylesheet has asynchronously loaded." );
});
Usage Tips
We typically use loadCSS
to load CSS files that are non-critical to the first rendering of a site. See the EnhanceJS project Readme for examples of how we typically use it to improve page loading performance.
The reason this script is sometimes necessary is because there is no native way in HTML (currently at least) to load and apply a CSS file asynchronously. CSS references that use either link
or import
will cause browsers to block page rendering by default while their related stylesheet loads.
Contributions and bug fixes
Both are very much appreciated - especially bug fixes. As for contributions, the goals of this project are to keep things very simple and utilitarian, so if we don't accept a feature addition, it's not necessarily because it's a bad idea. It just may not meet the goals of the project. Thanks!