Using CSS vs JavaScript for external link icons

Written by Richard Heyes, on 26th November 2022

Introduction

Here's a little snippet that I recently had the fortune of learning. The thing that I found out was how to use images with the css content property. Now, if you just specify the path, obviously it would use that as the text and if you give the whole tag (ie content: '<img src="/images/myImage.png" />' ) it just prints the tag out verbatim. So what to do?! Well that's where the url() function comes in to save the day. Consider:

Instead of doing this: 

content: '<img src="/images/myImage.png" />'

You would do this: 

content: url('/images/myImage.png');

The previous JavaScript version

So this is the previous code that I was employing, making use of jquery, to get all of the links on the page, check if they're external links and then replace the text [icon] (if it's present) with the <img> tag for the image. 

(function ()
{
    // Get all of the links (using jQuery - feel free to get the links however you please)
    $links = $('a');

    // Loop through all of the links
    for (var i=0; i<$links.length; ++i) {
        
        // Get the href attribute from the current link
        var href = $links.eq(i).attr('href');
        
        // Get the rel attribute from the current link
        var rel  =  $links.eq(i).attr('rel');

        // If this link:
        //   1. Has href and rel attributes
        //   2. Starts with http:// or https://
        //   3. Isn't linking to a page on this website
        //   4. The rel attribute has the word external in it
        if (href && rel
            && href.match(/^https?:\/\//)
            && !href.match(/https?:\/\/(www\.)?rgraph\.net/)
            && rel.match(/external/)) {

            // Set the HTML inside the link to whatever is there currently
            // whilst replacing the text "[icon]" with the  tag for the
            // icon.
            $links.eq(i).html(
                $links.eq(i).html().replace(/\[icon\]/,'<img src="/images/external-link.png" width="12" height="12" style="margin-left: 5px" alt="This is an external link" />')
            );
        }
    }
})();

The new CSS version

So that was not an inconsiderable amount of JavaScript to use to add the image to links and now here's an alternative css version that's far more concise. It uses a few css operators that you may not have seen or used before - the square brackets make the browser look for <a> tags that have the rel attribute set to external (the *= operator instead of just = denotes that the word external can appear anywhere within the rel attributes value. And the ::after selects a pseudo-element that is added just after the element (the <a> tag in this case). The content property specifies what goes inside the ::after pseudo-element). Normally this might be a bit of text but here we've used the url() function to give the location of the image to use. 

/* Select the ::after peudo-element that appears after the a tag */
a[rel*="external"]::after {
    
    /* Specify the URL of the image to appear */
    content: url('/images/external-link.png');
    
    /* Add a bit of spacing */
    padding-left: 5px;
}

Using an SVG image instead of a PNG

Additionally, instead of using an external png image file as the image here's a version that uses an embedded svg file. It's a bit more css code but does mean that no image file is necessary. Thanks to Christian Oliff for this alternative. 

a[rel*="external"]::after {    
    content: "";
    width: 13px;
    height: 13px;
    margin-left: 4px;
    margin-bottom: 2px;
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='13' height='13' fill='currentColor' viewBox='0 0 16 16'%3E%3Cpath fill-rule='evenodd' d='M8.636 3.5a.5.5 0 0 0-.5-.5H1.5A1.5 1.5 0 0 0 0 4.5v10A1.5 1.5 0 0 0 1.5 16h10a1.5 1.5 0 0 0 1.5-1.5V7.864a.5.5 0 0 0-1 0V14.5a.5.5 0 0 1-.5.5h-10a.5.5 0 0 1-.5-.5v-10a.5.5 0 0 1 .5-.5h6.636a.5.5 0 0 0 .5-.5z'/%3E%3Cpath fill-rule='evenodd' d='M16 .5a.5.5 0 0 0-.5-.5h-5a.5.5 0 0 0 0 1h3.793L6.146 9.146a.5.5 0 1 0 .708.708L15 1.707V5.5a.5.5 0 0 0 1 0v-5z'/%3E%3C/svg%3E");
    background-position: center;
    background-repeat: no-repeat;
    background-size: contain;
    display: inline-block;
}

Conclusion

So a total of 3 lines of css compared to roughly 15 lines of javascript. Far shorter and easier to understand. You could add a comment explaining the css selector - especially if you're working in a team environment because it's not overly common so it might not be familiar to everyone.

Thanks go to Kevin Powell on YouTube without whom (and his videos) I wouldn't have learnt this technique. He makes a large amount of css and javascript videos - ideal if you're a budding or existing front-end developer. Cheers!