How to load up CSS files using Javascript?

How to load up CSS files using Javascript?

Is it possible to import css stylesheets into a html page using Javascript? If so, how can it be done?
P.S the javascript will be hosted on my site, but I want users to be able to put in the tag of their website, and it should be able to import a css file hosted on my server into the current web page. (both the css file and the javascript file will be hosted on my server).

Solutions/Answers:

Solution 1:

Here’s the “old school” way of doing it, which hopefully works across all browsers. In theory, you would use setAttribute unfortunately IE6 doesn’t support it consistently.

var cssId = 'myCss';  // you could encode the css path itself to generate id..
if (!document.getElementById(cssId))
{
    var head  = document.getElementsByTagName('head')[0];
    var link  = document.createElement('link');
    link.id   = cssId;
    link.rel  = 'stylesheet';
    link.type = 'text/css';
    link.href = 'http://website.com/css/stylesheet.css';
    link.media = 'all';
    head.appendChild(link);
}

This example checks if the CSS was already added so it adds it only once.

Put that code into a javascript file, have the end-user simply include the javascript, and make sure the CSS path is absolute so it is loaded from your servers.

VanillaJS

Here is an example that uses plain JavaScript to inject a CSS link into the head element based on the filename portion of the URL:

<script type="text/javascript">
var file = location.pathname.split( "/" ).pop();

var link = document.createElement( "link" );
link.href = file.substr( 0, file.lastIndexOf( "." ) ) + ".css";
link.type = "text/css";
link.rel = "stylesheet";
link.media = "screen,print";

document.getElementsByTagName( "head" )[0].appendChild( link );
</script>

Insert the code just before the closing head tag and the CSS will be loaded before the page is rendered. Using an external JavaScript (.js) file will cause a Flash of unstyled content (FOUC) to appear.

Solution 2:

If you use jquery:

$('head').append('<link rel="stylesheet" type="text/css" href="style.css">');

Solution 3:

I guess something like this script would do:

<script type="text/javascript" src="/js/styles.js"></script>

This JS file contains the following statement:

if (!document.getElementById) document.write('<link rel="stylesheet" type="text/css" href="/css/versions4.css">');

The address of the javascript and css would need to be absolute if they are to refer to your site.

Many CSS import techniques are discussed in this “Say no to CSS hacks with branching techniques” article.

But the “Using JavaScript to dynamically add Portlet CSS stylesheets” article mentions also the CreateStyleSheet possibility (proprietary method for IE):

<script type="text/javascript">
//<![CDATA[
if(document.createStyleSheet) {
  document.createStyleSheet('http://server/stylesheet.css');
}
else {
  var styles = "@import url(' http://server/stylesheet.css ');";
  var newSS=document.createElement('link');
  newSS.rel='stylesheet';
  newSS.href='data:text/css,'+escape(styles);
  document.getElementsByTagName("head")[0].appendChild(newSS);
}
//]]>

Solution 4:

Call the following function to dynamically load CSS or JavaScript file.

function loadjscssfile(filename, filetype) {
  if (filetype == "js") { //if filename is a external JavaScript file
    // alert('called');
    var fileref = document.createElement('script')
    fileref.setAttribute("type", "text/javascript")
    fileref.setAttribute("src", filename)
    alert('called');
  } else if (filetype == "css") { //if filename is an external CSS file
    var fileref = document.createElement("link")
    fileref.setAttribute("rel", "stylesheet")
    fileref.setAttribute("type", "text/css")
    fileref.setAttribute("href", filename)
  }
  if (typeof fileref != "undefined")
    document.getElementsByTagName("head")[0].appendChild(fileref)
}

Pass the complete file path with the name as filename argument.

Solution 5:

I know this is a pretty old thread but here comes my 5 cents.

There is another way to do this depending on what your needs are.

I have a case where i want a css file to be active only a while. Like css switching. Activate the css and then after another event deativate it.

Instead of loading the css dynamically and then removing it you can add a Class/an id in front of all elements in the new css and then just switch that class/id of the base node of your css (like body tag).

You would with this solution have more css files initially loaded but you have a more dynamic way of switching css layouts.

Solution 6:

If you want to know (or wait) until the style itself has loaded this works:

// this will work in IE 10, 11 and Safari/Chrome/Firefox/Edge
// add ES6 poly-fill for the Promise, if needed (or rewrite to use a callback)

let fetchStyle = function(url) {
  return new Promise((resolve, reject) => {
    let link = document.createElement('link');
    link.type = 'text/css';
    link.rel = 'stylesheet';
    link.onload = function() { resolve(); console.log('style has loaded'); };
    link.href = url;

    let headScript = document.querySelector('script');
    headScript.parentNode.insertBefore(link, headScript);
  });
};